Abstract: Light and elevated temperature degradation（LeTID）is a non-negligible phenomenon of efficiency degradation in silicon solar cell. However,the exact mechanism of the degradation and the evolution process of related defect still need to be clarified. In this paper,we analyzed the evolution of degradation and regeneration under different light intensity in p-type multi-crystalline silicon passivated emitter and rear contact（PERC）solar cell. It shows that illumination accelerates the degradation and the regeneration reaction,but the decrease in light intensity improves the degradation degree. The result shows that there are two main defects inducing SRH（Shockley-Read-Hall）recombination in the bulk of silicon during the degradation-regeneration cycle. The deep level defect dominants SRH recombination in the bulk with ratio of electron to hole capture cross-sections k in the range of 33 ＜ k ＜ 37,and the shallow level defect with less influence during the whole cycle may be Fe—B complex with k value between 0.1 and 1.