Abstract: This paper focuses on the problem of junction box bulging in PV modules of an outdoor PV power station in Northwest China.Normal PV modules are removed and sent to the laboratory for simulation testing and analysis of thermal performance under short-circuit current of the junction box bypass diode.The results indicate that after the thermal runaway test,the performance of the junction box bypass diode can still meet the requirements of relevant international standards.The junction box bulging is not directly related to the thermal performance of the reverse current overload of the bypass diode,but it is related to the thermal performance under long-time short-circuit current (I_sc).At 2.5I_sc,the bypass diode of the junction box generates a high temperature exceeding 220℃，and the accumulated heat causes the sealing adhesive to turn yellow and melt,resulting in bulging failure of the junction box.