Abstract: Light induced degradation（LID） and light and elevated temperature induced degradation（LeTID） are two main degradations of crystalline silicon solar cells,with typical light soaking conditions of 25 ℃ and 1 sun（LID environment）and 75 ℃ and1 sun（LeTID environment）,respectively. In this paper,the degradation mechanism of p-type cast mono silicon wafer was studied by the effective minority carrier lifetime. At 200 ℃ and 7 suns,the minority carrier lifetime of the sample decreased first and then recovered. This process was called the light soaking regeneration. In LID environment,the samples without light soaking regeneration had two degradation stages:fast and slow,but the samples with light soaking regeneration only had the fast degradation stage. The electron/hole capture cross-section ratio of the LID defect near the center of the bandgap was calculated to be about 7,indicating that the defect was the same as the BO defect in Czochralski silicon（Cz-Si）. For the samples with light soaking regeneration,the k is calculated to be about 35 at the maximum LeTID stage,indicating that LeTID defect in cast mono silicon is similar with that in multicrystalline silicon（mc-Si）.