Abstract: Based on the typical successful path and the required load capacity for the removal of residual heat for the nuclear power plants in Qinshan region, three different methods are adopted to calculate the diesel generator capacity and analyze the selection. Selection of the diesel with smaller capacity and the generator with larger capacity can satisfy the allowable bus voltage drop when the plant directly starts the large capacity motor. It solves the difficult problem that the large capacity diesel cannot be incorporated into a mobile diesel generator vehicle. This paper analyzes the main considerable factors for a mobile diesel generator vehicle, such as the emergency and test selection switch.