The status quo and existing problems of monitoring system for EV battery swap station are analyzed. Then a modified intelligent monitoring system for EV battery swap station is designed, combined with the actual battery swap operation process. The monitoring system solves the difficulty of electric energy metering and billing for battery swap by means of the design of a new battery swap electric energy metrological method. The monitoring system solves problem of the insufficient intelligent degree of monitoring system for EV battery swap station by designing a battery box optimization strategy, which realizes the application of auto battery swap control command send, battery swapping process management, panoramic inversion of decision making and execution process of battery swap, etc. This paper designs the system composition, architecture design, functional definition, and new battery swapping process of the battery swap monitoring system, finally realizes the monitoring system through the work on software design, network realization, data structure, battery swapping electric energy metering and billing, and the auto battery swap strategy. Practical project application results show that, the proposed monitoring system can significantly reduce the complexity and cost of battery swap electric energy metering and billing, effectively improve the intelligent degree of monitoring system for EV battery swap station, and lower the construction and operating costs of EV battery swap station. This work is supported by National Key Research and Development Program of China (No. 2016YFB0101800) and National Invention Patent of China (No. CN106183864A).