The Westgate development in the city centre will eventually have more than 100 shops, 25 restaurants and cafes, a cinema and 61 flats.
The multi-storey car park on the site was demolished last year. It will be replaced with a 1,000-space underground car park.
The development is due for completion in autumn next year.
It will include rooftop terrace dining and new public spaces.
Site owner Westgate Oxford Alliance, a joint venture between commercial property company Land Securities and The Crown Estate, said the development would cover 800,000 sq ft (74,322 sq m) when complete.
Preparatory work began in February 2015 following planning approval by Oxford City Council.

The X-47B jet is being designed by weapons manufacturer Northrop Grumman for the US Navy.
It was in the air for 29 minutes during its maiden flight and reached an altitude of 5,000 feet.
Officials say it will help form part of a new generation of unmanned drones and works like a smaller version of the B-2 Stealth Bomber.
As such it would be very different from the current fleet of remote controlled military planes like the Predator and Reaper.
Instead the X-47B would be virtually invisible to radar and fly at much faster speeds than those older, propeller driven machines.
In a statement Captain Jaime Engdahl, a programme manager for the warplane, said: "Today we got a glimpse towards the future as the Navy's first-ever tailless, jet-powered unmanned aircraft took to the skies."
The flight was primarily designed to test the jet's guidance and navigation systems and the aerodynamic control of the tailless design.
It was controlled from the ground by a joint team of the company's engineers and Navy specialists.
Northrop is building the bomber as part of a Â£395 million contract signed in 2007.
Janis Pamiljans is vice-president of Northrop Grumman's Aerospace Systems sector.
"Designing a tailless, fighter-sized unmanned aircraft from a clean sheet is no small feat.
"Commitment, collaboration and uncompromising technical excellence among the Navy [and] Northrop Grumman made today's flight a reality.
"We are indeed honoured to have given wings to the Navy's vision for exploring unmanned carrier aviation."
Although it will be several years before the X-47B is ready for operations officials say it should have its first test flight from an aircraft carrier in 2013.
Follow Radio 1's technology reporter Dan Whitworth on Twitter

Last week, the 31-year-old Brighton midfielder was named in the Wales squad for their upcoming friendlies, over two years after his last call-up.
"Wales manager Chris Coleman said to have a better chance of going in the summer he'd like to see me playing regularly," Crofts told BBC Radio Kent.
"I wasn't guaranteed that with Brighton, so it was a tough decision."
Crofts has featured 18 times for the Seagulls, who are second in the Championship, this season but his last outing came in the defeat by Cardiff on 20 February.
The former Norwich man has won 27 caps for Wales, with the last of those coming against Serbia in September 2013.
However, he could add to those in the friendlies against Northern Ireland and Ukraine during the international break.
"With the Euros coming up for Wales it was important for me to get some games under my belt before the end of the season," he added.
"After speaking to Chris, my place isn't guaranteed even if I play, but it gives me the best opportunity."
Crofts began his career at Gillingham and has returned to Priestfield Stadium until the end of the campaign, although Brighton have a 28-day recall clause as part of the deal.
He scored 19 goals in 191 games in his first stint at the Kent club and he hopes he can help the Gills, who are fourth in League One, win promotion to the Championship.
"This year I have got three massive goals; Brighton to get promoted, Gillingham to get promoted and a place at the Euros," he said.
"I am going to work as hard as I can to achieve those things. I'll give it everything I have got."

22 May 2017 Last updated at 07:13 BST
A team of researchers say they've come up with a new exercise that cuts the risk of kids getting hurt when playing rugby.
The exercise could now be introduced in schools.
Watch Jenny's report for more.
Work has begun to demolish a 1970s shopping centre in the centre of Oxford as part of a £440m redevelopment.
[NEXT_CONCEPT]
Military chiefs in America say a new, unmanned stealth bomber has carried out its first test flight.
[NEXT_CONCEPT]
Andrew Crofts says his ambition to play at Euro 2016 is part of the reason for his loan move to Gillingham.
[NEXT_CONCEPT]
Rugby is not the most gentle of sports and it's been hitting the headlines because of some bad head injuries.