Abstract: The generation side of China's electricity spot market has a high market concentration, and identifying the abuse of market power has become particularly important. This article provides a detailed overview of the identification methods for the ex-ante market power in the United States. It analyzes and points out that the behavior-impact testing method suits China's electricity spot market more. On this basis, this article further studies and proposes ex-ante and ex-post market power identification methods under high market concentration, including residual supply indicator testing method and market simulation method for identifying potential market power, a behavior-impact testing method for identifying market power during events, and post-event market power identification method for comprehensive evaluation from four dimensions: overall market operation, user side, power generation side, and grid side. Finally, the rationality and feasibility of the market power identification method proposed in this paper were demonstrated through numerical analysis.