With the development of a new round reform of the electricity market in China, medium and long term electricity market has been gradually liberalized. Under the state of spot market being gradually started, how to bid in market becomes the key of development for power provider. This paper introduces the electricity market in new round reform, analyzes the currently existing electricity price forecasting method and bidding ways, and researches the day-ahead electricity market bidding strategies. Combining the historical price, environmental and economic factors, this paper proposes an electricity price forecasting method based on the similar day principle and the support vector machine algorithm. In consideration of the cost of thermal power units and bidding risk, this paper puts forward day-ahead market bidding strategies for units, and uses advanced particle swarm optimization algorithm-differential evolution (PSO-DE) hybrid algorithm to optimize bidding results. The results show that the proposed strategy can be applied to the electricity market bidding, which has a certain reference significance for the development of power spot market and power generation enterprises.