In order to accurately predict the flow and heat transfer characteristics in the engine nozzle, the Navier-Stokes equation and the renormalization group (RNG) k-ε turbulence model were used as the basis for the transient numerical simulation of the flow and temperature field in the nozzle by the computational fluid dynamics software Fluent. The calculation results show that in the initial stage of combustion in the engine, the fuel gas in the nozzle flows at a subsonic speed, and the overall temperature of the nozzle is still relatively low. As time goes on, shock waves begin to appear in the nozzle, and this is accompanied by the sudden decrease in the gas speed, and the sudden increase in the gas temperature. Due to the impact of the shock wave, the airflow forms a low-speed and high-temperature region in the downstream of the shock wave. As the gas expands, the shock wave gradually moves out of the nozzle, and the fuel gas in the nozzle flows at a supersonic speed, and the overall temperature of the nozzle is high. The research results can provide some references for the design and optimization of the engine nozzle.