The efficiency of a photovoltaic power station is affected by many factors. If various influencing factors can be comprehensively considered and the power generation of photovoltaic power stations can be estimated in advance, it is then possible to increase the efficiency and hence the economic benefits of photovoltaic power stations in operation. In this paper, a comprehensive evaluation model is proposed for evaluating the photovoltaic power generation efficiency. Many influence factors, such as light conditions, ambient temperature, relative air humidity, and attenuation characteristics of different photovoltaic modules, are considered in the proposed model. A simulation analysis of design parameters and environmental conditions was carried out on a 20MW photovoltaic power station. The simulation results show that the proposed evaluation model can efficiently reflect the correlation of influence factors and the efficiency of the photovoltaic power station. The evaluation model can be used to predict the efficiency of photovoltaic power stations in the planning and design stages.