The invention provides a system of measuring generating power of photovoltaic modules. The system comprises a plurality of photovoltaic modules, a photovoltaic module measurement device, a gateway, a direct current combiner box, a direct current distribution cabinet, an inverter, an environment monitor, and a data processing unit. The photovoltaic module measurement device is connected with the photovoltaic modules. The gateway is connected with the photovoltaic module measurement device. The direct current combiner box is connected with the photovoltaic modules and the photovoltaic module measurement device. The direct current distribution cabinet is connected with the direct current combiner box. The inverter is connected with the direct current distribution cabinet. The data processing unit is respectively connected with the gateway and the environment monitor and used for receiving voltage and current of the photovoltaic modules, receiving the total irradiance, direct irradiance, diffusivity, environmental temperature, module temperature and wind speed of the horizontal plane, and outputting generating power of the photovoltaic modules. The system has the advantages that the demands of the photovoltaic generating system for module operating state and generating power analysis are met, operating states and generating states of the photovoltaic modules are known timely, and generated power loss is reduced.