The power generation efficiency of photovoltaic (PV) module is affected by various factors, and temperature is one of the important factors. The influence of temperature on the efficiency of PV module is analyzed based on the linear regression model between them. The existing researches usually only consider the influences of irradiation, wind speed, installation structure and location on the PV module temperature, and neglect the influence of durative high radiation on the PV module which continues to work in the high power generation state, resulting heat accumulation and the module temperature increment over time. In this paper, it is validated that one of the reasons of PV module temperature increase over time is heat accumulation in sunny days by analyzing the measurement data of roof-mounted PV power plant, which will have negative effect on efficiency. The rain plays the role of cooling solar panels, so that efficiency is less affected. Based on this, time is added as another factor of the typical multivariate linear model of power generation efficiency to construct more accurate models for different weather types.