The turbine operated in full load and fault-free for 7.5 hours, with a maximised operational load of 5.134MW, said Dongfang. It was connected to the grid on 1 June.
The design, which has a 140-metre rotor, is also being used by Hyundai Heavy Industries.
It was put into full-load test and passed low-voltage ride-through test in the factory in Deyang, Sichuan province, on 20 February.
AMSC has chosen GL Renewables Certification to conduct the A-Design Assessment of its 5.5MW offshore turbine design for China's Dongfang Electric.
Dongfang originally announced it was building the turbine in July 2012. The first prototype was installed in a wind farm in Nantong, east China's Jiangsu province, for testing late this year.
The turbine is jointly designed and developed with AMSC. Dongfang hopes to sell the 5.5MW offshore wind turbines to the overseas market.
An Hui, general manager of the wind power division of Dongfang, said the company hopes to raise its share of the Chinese market to 15% by 2015.