Energy saving and emission reduction has always been a hot issue that countries in the world continue to care about. The triple-generation system of combined cooling, heating and power system is widely used because of its higher primary energy utilization. For the capacity allocation and operation mode planning of the combined cooling, heating and power system, a comprehensive evaluation index considering exergy loss is proposed as the objective funetion of optimization, and the function optimizes the system from three aspects of high efficiency, economy and low emission. Taking the capacity and operation mode of the gas turbine as design variables, the research model of capacity allocation and operation mode of triple-generation system is established. This method is applied to the co-generation system of a hotel building for analysis and planning. The research results show that the optimal capacity of the gas turbine is 200 kW , and the combinaion of heat and power is the optimal operation mode. Under this mode, the combined cooling, heating and power system has a 3.5 % lower exergy loss rate than the traditional energy supply system; the annual comprehensive emissions is reduced by 593. 7 t; the annual economic cost is saved by 298 000 yuan. This method can comprehensively and objectively analyze the system performance under a certain capacity and certain operation mode , which provides a reference for solving the operation planning problems of the combined cooling, heating and power system.