The $43bn (£33bn) deal is set to be the biggest ever foreign takeover by a Chinese company.
The deal was cleared by the Committee on Foreign Investment in the United States (CFIUS) which checks deals for national security implications.
About a quarter of  Syngenta's sales are in North America.
China National Chemical Corporation offered $465 per share for Syngenta in February. Syngenta's shares subsequently fell to about 20% below that because of concerns that CFIUS would not clear the deal.
However, now competition authorities elsewhere are expected to give the deal the go-ahead.
In a joint statement, Syngenta and ChemChina said: "In addition to CFIUS clearance, the closing of the transaction is subject to anti-trust review by numerous regulators around the world and other customary closing conditions.
"Both companies are working closely with the regulatory agencies involved and discussions remain constructive. The proposed transaction is expected to close by the end of the year."
When the deal was announced earlier this year, Syngenta chairman Michel Demaré said that it would help the company's pesticides and seeds business to expand further in China.
"ChemChina has a very ambitious vision of the industry in the future," he said. "Obviously it is very interested in securing food supply for 1.5 billion people and as a result knows that only technology can get them there."
The Chinese company owns a variety of businesses, included the Italian tyre maker Pirelli, German machinery-maker KarussMaffei and Israel's biggest pesticides producer.
The deal would be the second-biggest takeover in the chemicals industry in the past year after the $130bn Dow Chemical-DuPont merger announced last December.

Turia Pitt received burns to 65% of her body and was told she would never compete again after the 2011 ultra-marathon in Western Australia.
After 200 operations, she completed the 226km (140 mile) Hawaii event on Sunday
She has been hailed on social media as an "amazing role model".
Find out how to get into triathlon in our special guide.
Ms Pitt completed a 3.8km swim, 180km bike ride and 42km run in a time of 14:37:30.
The mining engineer, author and motivational speaker completed the event using custom-made gear and brake levers on her bike to accommodate the severe injuries to her hands.
She also wore special race clothing to deal with the extreme heat and humidity.
"Because of my burns, I can't regulate my own body temperature so I've had to make some adjustments, or use standard tri gear in different ways," she revealed last month.
"I'm going to need things like cooling sleeves and white suits so I don't overheat."
After her encounter with the bushfire Ms Pitt spent 864 days in hospital and underwent many operations to treat her injuries.
She made her comeback in the Ironman Australia triathlon in May.
"Competing in Ironman has ultimately showed me that I literally can do anything I put my mind to," she said on her blog.
Ms Pitt was widely praised on social media as an inspiration.
"Such a great example of what can be done through hard work belief in one's self and good a support system," one person wrote on her Facebook page.
"You continue to amaze and inspire," said another.
Shares in Swiss agribusiness group Syngenta have risen 12% after its takeover by ChemChina was given the go-ahead by a US regulator.
[NEXT_CONCEPT]
An Australian runner who suffered life-threatening burns when she was trapped by a bushfire during a race has completed the Hawaii Ironman, seen as the world's toughest triathlon.