The invention provides a method and system for performance determination of a photovoltaic module. According to the historical data, the function model between the output power of the photovoltaic module and the external temperature and illumination intensity is given. Then the measured temperature and illumination intensity are substituted into the model to obtain the ideal output power of the photovoltaic module. Finally, the ideal output power and the actual output power are calculated by scoring function, and the final performance evaluation value is given. Compared with the closest existing technology, this method can realize the real-time performance evaluation of components, and overcome the shortcomings of the traditional evaluation methods which require strict test conditions.