As people pay more and more attention to greenhouse gases and limited resources, solar energy is widely used as a clean energy source. The performance ratio of PV systems is easily influenced by the various environmental andtechnical factors, theresearch on theperformance analysis ofPVmodule isina need. This work isaimed at studying the performance parameters under STC, EL images and dark I-V curves to explore the output characteristic of polycrystallinemodules based on the faults in thecase of electrical overload and mechanical stress. The resultsshow that three defective bypass didoes mainly affected the open circuit voltage, voltage at MPP, power at MPP, current at MPP except theshort circuit current. Meanwhile, there isnoEL signal inthefaulty modulewith threedefective bypass diodes. When the cracks appear at the beginning, it causes small effect on the performance degradation of PV module. The inflection point from dark I-V curves under electrical overload drops significantly than mechanical stress, which causes more power losses.