Abstract:The meteorological factors such as temperature, air pressure and relative humidity have a significant impact on summer electricity load. In order to quantitatively study the change of electricity load caused by meteorological factors, the summer air-conditioning load is defined as the difference between the summer electricity load and the average electricity consumption in April and September of the year. The meteorological data in Nanjing from January 2014 to December 2016, consisting of the hourly temperature, air pressure, relative humidity, water vapor pressure, rainfall, wind speed, dew temperature, and the hourly daily electricity load data, are used to forecast air conditioning load by using five machine regression algorithms including multivariate linear, K-Nearest neighbor, decision tree, bagging regression and random forest for modeling and optimizing the parameters, respectively. The results show that the multiple linear regression method performs worst among the five machine regression algorithms, but increasing the number of parameters' types and samples can improve the forecast accuracy. Random forest regression algorithm is the most effective method of the five machine regression algorithms, which reduces the error rate by 44% compared with the multiple linear regression, better describes the extreme conditions of high air-conditioning load and reduces the overfitting phenomenon of the training data.