Abstract: The differences between balanced maintenance and conventional vehicle maintenance in Metro design code are expounded from the aspects of maintenance procedure and process. The number of allocated vehicles under balanced maintenance mode and conventional maintenance mode is calculated and compared, which further determines the design scale of vehicle base based on balanced maintenance. Research results show that after adjusting the traditional scheduled maintenance, biweekly inspection and seasonal inspection to balanced maintenance+specialized maintenance, the maintenance time can be effectively reduced, and the number of vehicles allocated to the whole line can be reduced accordingly, so as to reduce the design scale of the vehicle base and project investment.