The invention discloses a lithium battery SOC estimation method based on a Takagi-Sugeno fuzzy model. A second-order equivalent circuit model of a lithium battery is established, and linearized to obtain sub linear module models, a proper membership function is selected for each sub linear model, a system observer is designed after normalization, a linear matrix inequality is solved, a feedback gain of the observer is obtained, and the SOC of the lithium battery is obtained. According to the invention, linearized analysis theories and methods are introduced into SOC estimation of the lithium battery, direct analysis on a nonlinear lithium battery model and direct observer design are avoided, and the precision is higher compared with a traditional lithium battery SOC estimation method.