The cycle life of lithium titanate battery is an important performance evaluation index. In this paper, the soft coated lithium titanate battery is taken as the research object, and the cyclic aging test is carried out at room temperature. The causes of capacity attenuation and internal resistance increase in the whole life cycle of the battery are analyzed through the in-situ analysis methods such as voltage differential analysis and capacity increment analysis, and a residual capacity estimation method based on characteristic parameters is proposed. According to the comprehensive analysis, the main reasons for the capacity decline of lithium titanate battery are the loss of cathode materials and lithium ion, while the reason for the accelerated capacity decline at the end of the battery life is the sharp increase of the internal resistance of the battery.