As a non-negligible part of light and elevated temperature induced degradation (LeTID), the studies of surface related degradation are rare, and the complex mechanism hinders the research in this field. In this paper, the degradation behaviors of passivation quality on the surface of P-type multi-crystalline silicon were mainly analyzed during LeTID. Results shown that effective minority carrier lifetime of passivated mc-Si wafers decreased in the range of 20-50% after it got to the full degraded during light soaking at 80 degrees C. The fixed charges at the interface between passivation layer and silicon bulk increased slightly after full degradation, which had little effect on field-effect passivation. Long-term illumination resulted in a certain increase in interface states density (Dit) in the bottom half of bandgap. According to the result that the increment of Dit of ungettered samples was higher than that of phosphorus diffusion gettered samples, it implied that the increase of interface defects might be caused by the diffuse of impurities in the bulk to the surface during the process of LeTID.