Abstract: The thermal protection of rocket engines is a crucial aspect of rocket engine design. In this paper the gas film/ regenerative composite cooling of the LOX(liquid oxygen)/LCH4(liquid methane) rocket engine thrust chamber is investigated. A gas film/regenerative composite cooling model was developed based on the Grisson gas film cooling efficiency formula and the one-dimensional regenerative cooling model. The accuracy of the model was validated through experiments conducted on a 6 kg/s level gas film/ regenerative composite cooling thrust chamber. Additionally, key parameters related to heat transfer performance were calculated. The results demonstrate that the model is sufficiently accurate to be used as a preliminary design tool. The temperature rise error of the coolant, when compared with the experimental results, was found to be less than 10%. Although the pressure drop error is relatively large, the calculated results still provide valuable guidance for heat transfer analysis. In addition, the performance of composite cooling is observed to be superior to regenerative cooling. Increasing the gas film flow rate results in higher cooling efficiency and a lower gas-side wall temperature. Furthermore, the position at which the gas film is introduced greatly impacts the cooling performance. The optimal introduction position for the gas film is determined when the film is introduced from a single row of holes. This optimal introduction position results in a more uniform wall temperature distribution and reduces the peak temperature. Lastly, it is observed that a double row of holes, when compared to a single row of holes, enhances the cooling effect in the superposition area of the gas film and further lowers the gas-side wall temperature. These results provide a basis for the design of gas film/regenerative composite cooling systems.