Abstract: Numerical solutions of full Navier-Stokes equations with chemical reaction flow were established for the nozzle flow of the LOX/HTPB hybrid rocket motor.Lower-Upper decomposition scheme and MUSCL-type and VanLeer approach were used.A chemical reaction model with 8 components and 10 elementary reactions was presented.The nozzle entrance condition was obtained by thermodynamic calculation.The nozzle flows under several different oxidizer mass flow rates and grain length were calculated.The relationship between oxidizer mass flow rate and specific impulse was analyzed,which will be useful for the hybrid rocket motor design.