The invention relates to the technical field of power batteries of electric automobiles, and discloses a composite estimating method of a power battery SOC based on a PNGV equivalent circuit model. The composite estimating method comprises the following steps that A, the open-circuit voltage of the power battery is detected; B, an open-circuit voltage method is used for calculating the primary SOC (t0) of the power battery; C, in the time period of t0-t1, an EKF algorithm is used for correcting the primary SOC (t0), and an SOC (t1) is obtained; D, in the time period of t1-t2, an improved ampere-hour integral method is used for estimating; E, when the power battery is continuously used, the steps from the step C to the step D are circulated; the t0 represents the primary time, and the t1 and t2 represent the time points after the t0. According to the composite estimating method of the power battery SOC based on the PNGV equivalent circuit model, the correction coefficients of influencing factors such as the charging and discharging currents of the power battery, the environment temperatures, the battery health state are considered, the improved ampere-hour internal method is used, and the defect that the influence from outside factors is large when the ampere-hour internal method is used for estimating the power battery SOC can be overcome. The advantage that an EKF method has a powerful correcting effect on initial errors of the SOC is fully used.