Abstract: Two experimental modules A and B are prepared by monocrystalline silicon cells, and the potential-induced degradation (PID) tests are carried out on the two experimental modules under the conditions of high temperature, high humidity and high bias voltage. The electroluminescence (EL) defect diagram of the modules show that the two modules appear the micro-cracks, broken grid and other defects with the progress of the test. The volt ampere (IV) characteristic performance results show that the degradation of the maximum power of modules A and B are 19.34% and 11.02% respectively after 192 h. The analysis results show that the leakage current of the modules is generated under the environment of high temperature, high humidity and high bias voltage, which leads to the migration of Na⁺ from the glass to the cells and affects the performance of the cells, which is the main reason for the performance degradation of the modules.