Abstract: To investigate radiation loss inside the low power argon Arcjet Thruster,numerical simulations and analyses were carried out by using radiation and no radiation models contrastively.Non-oscillatory and Non-free-parameters Dissipative finite difference scheme with second order accuracy was employed to solve Navier-Stokes equations coupled with electromagnetic and radiant source terms,and implicit residual-smoothing technique was adopted to accelerate numerical converging.Finite control volume integral approach was developed to discrete elliptic partial differential equation of electromagnetic field,and successive over relaxation method was introduced to expedite numerical converging.By virtue of numerical simulations,flow distributions within the thruster, thrust, specific impulse and thrust efficiency of the thruster in radiation and no radiation models are presented.Results of the study show that 0.137% lower specific impulse and 1.03% lower thrust efficiency are obtained in radiation model,compared with no radiation model,and radiation loss has little effect on performance of low power Arcjet Thrusters.