In power market， such uncertain factors have been introduced for generation investment decision-making as the competition from other generating companies（Gencos） and the variation of investment value， whose influences are usually neglected in traditional methods of generation expansion planning. Based on the Black-Scholes option pricing theory and non-cooperative game theory， a deferment option game model of generation investment is developed， which makes the strategies of Gencos’ generation investment more rational. The rationality and validity of the method proposed is illuminated by a practical test example.