Meteorological factors are important in short - term load forecasting. Considering the cumulative effect of meteorology,similar days are selected as training samples,a BP neural network load forecasting method based on improved particle swarm optimization algorithm ( IPSO - BP) is proposed . Firstly,the meteorological factors more relevant to daily loads are determined by means of correlation analysis. On this basis,the weighted geometric distance is used to select the historical days which have a greater correlation with the predicted day as the similar day,and the IPSO - BP neural network model is trained and used in short - term load forecasting. The practical application results show that the proposed prediction model and data processing method can achieve more accurate prediction results.