Abstract Cogeneration is internationally recognized as an important way to save energy and improve environment. At present, the cogeneration scale in China has been ranked at the second place all round the world. China formulated relevant laws, regulations and technology policies to actively encourage and support the development of cogeneration. This article selects 62 Northeast regional Chinese cogeneration enterprises' financial data from 2003 to 2007, and analyzes the impact of the electric power industry deregulation to cogeneration enterprises' performance by using a partial frontier nonparametric. Further more, we study whether the cogeneration enterprises actualize horizontal scope economy by comparing with the thermal power alone or heat production alone enterprises. Results show that the factory network separation and regional market trial reform can promote the cost efficiency of both five major power group cogeneration enterprises and independent cogeneration enterprises. Compared to five group enterprises, the scope economies index of the independent cogeneration enterprises is lower, the unbundling reform and northeast regional market trial reform have a negative impact on cogeneration enterprises to achieve scope economies and improve cost efficiency.