Gaseous fuel internal combustion engines (gas engines) for electric generating are important primary movers in distributed energy systems. However, the average thermal efficiency of the gas engine is just about 30%-40% and most of the waste heat is discharged by exhaust. So it is very meaningful to recover the exhaust waste heat. Electricity-cooling cogeneration system (ECCS) inclusive of a steam Rankine cycle (RC) and an absorption refrigeration cycle (ARC) is an effective way for recovering exhaust waste heat of gas engine. Partload performance analysis of ECCS is of great significance due to the frequently varied working conditions of gas engines in practical operation. In this paper, an off-design simulation model of ECCS is firstly established by Matlab. Then the effects of the engine working condition on the performance of ECCS are analyzed by this model. The results indicate that ECCS can improve the thermal efficiency of gas engine by 15.2%-16.9% from 40% to 100% working condition, which proves the excellent part-load adaptability of ECCS. Results would have guiding significance in practical operation of ECCS.