The electric supercharger can significantly increase the transient intake air charge of the engine, thus increasing the power output of the engine under heavy load conditions. However, the traditional in-cylinder intake air charge calculation model has heavy calibration workload and low portability, and is not suitable for the intake air charge calculation of the electric supercharged gasoline engine. In order to reduce the difficulty of in-cylinder intake air calibration and improve the accuracy of intake air estimation, based on an electric supercharged gasoline engine, this paper simplifies the actual intake process into valve overlap period and free intake period, and proposes an in-cylinder intake air charge estimation model with intake pressure sensor as the main load sensor based on the mean value engine model. Three unknown coefficients, i.e., residual exhaust gas correction coefficient ɑ1, heat transfer coefficient ɑ2 between manifold and fresh gas, and effective flow area ɑ3 in valve overlap period, are calibrated by using the simulation data of the numerical model of electric supercharged gasoline engine. Compared with the numerical simulation results, the air intake model established in this paper can accurately estimate the actual in-cylinder air intake of electric supercharged gasoline engine under the external characteristic condition, and the calculation error is within 5%, which can provide theoretical reference for the in-cylinder air intake estimation of electric supercharged gasoline engine