In present paper, the effect of combined cooling, heating and power generation systems(CCHP) in the reduction of pollutants emission have been investigated and a hotel with 80 rooms in Zahedan have been selected as case study , also gas engine (With part-load operation) as prime mover for design CCHP system. In this work is assumed that sell electricity to grid is possible. At the first phase, optimization for access to maximum reduce Pollutants emission have been done, at the other phase, a multi-criteria function has been introduced and the optimization process, with Percentage of Relative Annual Benefit (PRAB) has been investigated and the results of these two phases, have been compared together. Results show, CCHP systems have a high effect in reduce environmental pollutants emission CO, CO2 and NOx, as the percent reduce pollutants emission is positive in an extensive range of nominal power of gas engine. Also results show for access to maximum reduce pollutants emissions , CO2, CO and NOx, annual benefit as multi-ceritria objective function a gas engine with nominal power 2050kW is needed; in this case in addition to the most annual benefit also have a good effect for reducing Pollutants emission. In the end, the effect of the number of prime mover as designing parameter assessed with increase from one into two and three numbers. Results show increasing prime mover, cause decrease Relative Annual Benefit and pollutants emission.