The US National Highway Traffic Safety Administration closed its investigation after it found no evidence of a defect in the vehicle.
Joshua Brown was killed when his car collided with a lorry while operating in Autopilot mode.
Tesla has stated Autopilot is only designed to assist drivers, who must keep their hands on the wheel.
The feature is intended to be used on the motorway, where it lets cars automatically change lanes and react to traffic.
The NHTSA report said data from the car showed that "the driver took no braking, steering or other actions to avoid the collision".
Bryan Thomas from the NHSTA said the driver should have been able to see the lorry for seven seconds, which "should have been enough time to take some action".
The investigation did not find any evidence that the car's systems "did not perform as designed".
However, Mr Thomas said there was "industry-wide" concern about the way driver-assistance features were explained and advertised to customers.
"These systems require continual and full attention of the driver," he said.
"It's not enough to put [information] in the owner's manual and hope drivers are going to read that.
"Manufacturers must anticipate how drivers would use the functionality, and that some don't read the manual."
He said systems should be designed with the "inattentive driver" in mind.
The NHTSA said it would continue to monitor the safety of Autopilot and would take further action if necessary.
Mr Thomas warned manufacturers that if safety defects were found in semi-autonomous cars, they would have to be recalled, even if the vehicles were capable of receiving over-the-air software updates.
Following the closure of the investigation, Tesla's chief executive Elon Musk tweeted that the report was "very positive".

The supporters had been on a stadium tour but managed to cut themselves off from the remainder of the party.
They were found on Saturday morning during a security sweep of the stadium before being handed over to police, who decided not to arrest the pair.
United say there was no risk to supporters attending the Arsenal game.
The pair had been searched and their belongings put through a metal detector before they went on the tour.
The incident comes six months after United's Premier League game against Bournemouth at Old Trafford had to be called off at short notice when a suspect package was found in a toilet in the corner of the stadium.
It turned out to be a fake explosive left behind after a training exercise earlier in the week.

The 37-year-old led the Robins to last season's Challenge Cup final, but was sacked last month.
He replaces Australian Brian Smith, who resigned last week after winning just one of their first five games.
The Wildcats have also announced that Batley and Wales coach John Kear will join the club as director of rugby for the 2017 season.
Chester said: "I am delighted to become head coach of Wakefield Wildcats, especially as it is my home town club and a club with a lot of traditions.
"I have been stood on these terraces as a young kid and I am really proud that I now get to coach this great team."
Kear, who was appointed as Wales coach in July 2014 and will combine that post with his new role, added: "I am looking forward to joining the Wildcats and I will look to bring stability and improvement across the whole football department."
"My appointment at Wakefield in no way affects my role as head coach of Wales and I am looking forward to the Rugby League World Cup qualifiers this autumn."
Smith guided Wakefield to Super League survival with victory in the Million Pound Game against Bradford in October.
He signed a new one-year contract with the club after that, but left this month after a breakdown in his relationship with chairman Michael Carter.
Wakefield, who face Hull FC on Friday, are currently 11th in the 12-team Super League.
Tesla will not be ordered to recall its semi-autonomous cars in the US, following a fatal crash in May 2016.
[NEXT_CONCEPT]
Two Manchester United fans spent Friday night undetected in an Old Trafford toilet in an attempt to see Saturday's Premier League game against Arsenal.
[NEXT_CONCEPT]
Wakefield Trinity Wildcats have named former Hull KR boss Chris Chester as their new head coach.