With the support of powerful calculation ability of computer and Fluent of CFD software, integrative simulation research of the variable thrust liquid propellant rocket engine was developed. Numerical simulation of interior flow field of a variable thrust rocket engine with flux-oriented injector was done. The distributions of pressure, temperature, molar fraction of product and flow mach numbers were attained. By the contrast of the calculation results, the effects of structure parameters and working condition etc. on total whole performance of variable thrust rocket engine were analyzed. The results also provided theoretic references for design and optimization of variable thrust rocket engine.