Blade Electric Vehicle has get attention and support from the government with its greens environmental protection. With the rapid development of electric vehicle industry in China, the proportion of pure electric buses in cities is increasing rapidly, and it has been incorporated into the development plan of various regions. As we all kown, in the region dominated by thermal power, the implementation of electric buses is the transfer of carbon emissions to the power generation side, and can not achieve the true zero emissions. Therefore, the paper builds a pure electric vehicle carbon emission calculation model based on the same trip service with the consideration of line loss, charge and discharge efficiency and load factors. Then takeg Beijing city as an example, this paper calculate the reasonable power supply structure that is suitable for developing pure electric buses, which provides a reference for the development of regional pure electric buses.