Abstract: Common lithium battery capacity test methods have problems of low measuring precision, bad reliability, poor flexibility, the paper proposes a lithium battery capacity detection scheme with high accuracy based on internal resistance test method. In the paper, the relationship between lithium battery capacity and internal resistance is discussed, the estimation model of lithium battery charged state is established, and the hardware and software design of the system is completed. The system uses 4 wire AC inserting method to measure the intemal resistance of battery, and calculates the battery capacity according to the resistance. In addition, the system also achieves comprehensive testing and analysis of battery parameters, such as voltage, current, temperature.