The difference in user behavior of electric vehicles leads to different spatial and temporal distribution characteristics of electric vehicles. In order to accurately calculate the charging power and the demand response potential of electric vehicle cluster at a certain time and place, this paper proposes a method for calculating the charging power and demand response potential of electric vehicles based on space-time activity model. Firstly, the spatial and temporal distribution characteristics of electric vehicles are considered, and the travel activity model of electric vehicles is analyzed. Then based on the actual data, the distribution model of key influencing factors of electric vehicle charging is obtained. Finally, Monte Carlo and binomial distribution method are used to calculate the charging power curve of single electric vehicle and electric vehicle cluster on working days and non-working days, and the demand response potential are analyzed. The proposed algorithm can calculate the charging power of electric vehicles simply and quickly on the basis of taking into account the space-time distribution of electric vehicles. This work is supported by National Key Research and Development Program of China (No. 2016YFB0901100).