Although a Swiss company, a big chunk of Syngenta’s business takes place in the US and it is New York-listed meaning clearance by the Committee on Foreign Investment in the United States (CIFUS) was required.
At a value of US$43bn (£33bn), it would be the largest acquisition of foreign company so far by a Chinese firm.
About a quarter of Syngenta's sales are in North America.
ChemChina still needs European Union and Australian approval to complete the deal, though the US was seen by analysts as the major hurdle.
Last year, Syngenta rejected an offer from rival Monsanto in a cash and shell deal worth around US$45bn at the time.