Abstract: Photovoltaic/phase change material cooling system（PV/PCM）is regarded as research object in current study,the effects of fins spacing,fins thickness and length of external fins on the heat transfer performance of a PV/PCM cooling system are numerically investigated. Results indicate that the decreased fin spacing and the increased external fins length,can enhance the cooling effect and improve power generation of PV modules. Nevertheless,the fin thickness has little effect on the heat transfer of PCM. In addition,compared with the system without fins（Case 1）,melting duration of the system with fins spacing of 7.3 mm,fins thickness of 2 mm and external fins length of 25 mm（Case 2）,extends by 34.6%. Meanwhile,the decline rate of electrical efficiency of Case 2 slows down by68%,and the surface temperature reduced by about 30 ℃ after 180 minutes.