When the liquid propellant thruster works,its plume field would contain many propellant liquid droplets,especially at pulse state.Liquid droplets may move along with the gas flow and deposit on the components of spacecraft as contamination.The simulation of the plume field involving the gas molecules and liquid droplets is an important part in contamination studies of thruster plume.Based on the PWS software developed by Beihang University(BUAA),axial-symmetric two-phase direct simulation Monte Carlo(DSMC) method is used with the liquid droplet taken as a kind of solid particle.The computation of gas-to-particle effect and gas reflection on the particle surface are decoupled.The inter-particle collision is also considered.The gas parameters at nozzle exit of 120N engine after 20 ms pulse work are taken as the entrance condition of the numerical simulation.Four test cases are conducted for comparison of different collision modules.Simulation results show that the effects of liquid propellant droplets mainly concentrate near the axis line of engine.The particle-to-gas collision would cause evident differences in the gas field and subtle differences in the particle phase.The liquid droplets in the plume field are generally accelerated and convected by the gas molecules.The DSMC method is proved to be a feasible solver to numerically simulate the two-phase flow involving solid phase and rarefied gas flow. When the liquid propellant thruster works, its plume field would contain many propellant liquid droplets, especially at pulse state. Liquid droplets may move along with the gas flow and deposit on the components of spacecraft as contamination. The simulation of the plume field involving the gas molecules and liquid droplets is an important part in contamination studies of thruster plume. Based on PWS software developed by Beihang University (BUAA), axial-symmetric two-phase direct simulation Monte Carlo (DSMC) method is used with the liquid droplet taken as a kind of solid particle.The computation of gas-to-particle effect and gas reflection on the particle surface are decoupled.The inter-particle collision is also considered.The gas parameters at nozzle exit of 120N engine after 20 ms pulse work are taken as the entrance condition of the numerical simulation. Flow test cases are conducted for comparison of different collision modules. Simulation results show that the effects of liquid prope llant droplets mainly concentrate near the axis line of engine. The particle-to-gas collision would cause evident differences in the gas field and subtle differences in the particle phase. The liquid droplets in the plume field are generally accelerated and convected by the gas molecules The DSMC method is proved to be a substantially solver to numerically simulate the two-phase flow involving solid phase and rarefied gas flow.