The Hongyanhe plant is the first nuclear plant and the largest electricity producing facility in northeast China.
The $8 billion first phase of the project consists of four generating units with another two units planned for the second phase, China's Xinhua news agency said.
The plant is located near the town of Wafangdian, about 68 miles from the port of Dalian.
The first of the six units went on line Sunday afternoon, the Liaoning Hongyanhe Nuclea Power Co. said. The entire first phase will be completed by the end of 2015 and will have an annual capacity of 30 billion kilowatt hours, which will supply about 16 percent of the power used in Liaoning Province.