Based on two-fluid model,the gas-droplet flows in nozzle were studied numerically using variable step Runge-Kutta scheme.Heat interaction between the two phases was introduced in the model.The characters of subsonic and supersonic flows were analyzed,and the impacts of droplet size and initial void fraction on the flow field were investigated.Simulation results show that the liquid velocity increases more slowly compared with the gas velocity.With the decreasing droplet size,the exit liquid velocity increases,but the gas velocity decreases.Both gas and liquid velocities increase with the increasing initial void fraction.For the supersonic flow,the Mach number at the throat is less than 1,and the throat area decreases with the increasing initial void fraction and droplet size.The results are useful for the investigation on the performance of mist jet propulsion system.