With the deepening of market reform of power industry worldwide, power market plays an increasingly important role in determining electricity price and guiding supply and demand. However, due to the particularity of power industry, the actual electricity market is similar to an oligopoly market. Power companies may use their market forces to influence electricity prices and make big profits. This paper analyzes the market forces related problems in the power market. This paper summarizes the basic concepts of market power, establishes a market power monitoring framework, studies the monitoring methods of generators' withholding behavior, and introduces the practices of typical foreign electricity markets. Finally, combined with the special situation of China's electricity market, this paper gives recommendations to the operators and regulators of China's electricity market and provide ideas for reference.