Abstract: To investigate the influence of environmental pressure on arcjet thruster performance,computation of operating performance of a low power nitrogen/hydrogen arcjet thruster under various environmental pressures was performed.Non-oscillating and non-free-parameter dissipative finite difference scheme with second order accuracy and classical Runge-Kutta time-stepping scheme was used to solve Navier-Stokes equations coupled with electromagnetic source terms,and Gauss-Seidel over-relaxation iteration method was adopted to solve electromagnetic equation.The results present thrust,specific impulse and thrust efficiency of the thruster under various environmental pressures,as well as impulse density distribution on the exit plane.Analyses of the results demonstrate influence of the environmental pressure on arcjet thruster performance quantitatively,and provide reference for its experimental investigation and its space application.