On the basis of the conjugate gradient method, an inversion model of the transient convective heat transfer coefficient between the bore surface and the gunpowder gas is presented. In this study, the measured temperature at a certain depth from the bore surface is employed as input. The variation of the thermophysical properties of gun steel with respect to temperature is taken into consideration. After verifying the feasibility of the model with constant convective heat transfer coefficients, it is applied to the reconstruction of transient convective heat transfer coefficients that consistent with the classical interior ballistic laws. Results indicate that decreasing the measurement error and increasing the number of measurement points can effectively improve the performance of the model. As well, measurement points that placed further away from the inlet boundary offer superior accuracy. When studying the inverse heat transfer problem of the gun barrel, it is found that setting the monitoring time to be twice the duration of the interior ballistic period may guarantee sufficient input data. The inversion model may offer a promising theoretical framework for indirect measurement manner of the bore surface temperature of gun barrel.