There is a problem for liquid separation pipe joint of orbit and attitude control system that because the flow resistance and the steadystate flow force overload in the working process so as to influence its own and below engine work, therefore it is of significance to optimization and improvement of the liquid separation pipe joint. According to the position and working principle of the liquid pipe separation joint in a certain orbit and attitude control system, from the perspective of decreasing flow resistance and steady state liquid power, two kinds of liquid separation joints were designed and three different assemblies were adopted. Using the CFD software FLUENT, the internal flow field of the liquid separation joint pipe was analyzed and calculated. The results show that the second type and the first assembly method can make the liquid flow separation pipe internal flow field pressure distribution more uniform and evenly, let flow resistance and steady state liquid power be small. It indicates that the optimized internal structure of the pipeline is reasonable and logical which can meet the design requirements.