Abstract: Based on mass models and models of drift for pressure-feed, liquid propellant space engines system, optimization and analysis of combustion chamber pressures and gas tank shape are carried out in this paper. Some important conclusions are obtained: ① Total mass of the space engines system is reduced to a minimum with optimal pressure value of 1MPa; ② For the space engines system with annular gas tanks, the system mass is smaller and the drift of center of mass of a spacecraft is zero.