In order to research the effect of boron additions on precipitation phases of New Co base superalloy. to save cost and to short period. The precipitation phases of Co-8.8Al-9.8W alloy with different B content have been studied by Thermodynamic Simulation Calculation of JMatPro software. The result shows that the precipitation temperature and precipitation quantity of γ phase and μ-Co7W6 phase becomes lower while the content of B increases. whereas the precipitation temperature and precipitation quantity of η-Co3Al phase becomes higher. Finally, the result has been explained from the factors of boride phases and the effect of B on composition of precipitation. Interpretation indicates that with the increase of B content，content of each element of Solid-liquid equilibrium phase has a growing difference when γ phase precipitates ,lowering the temperature increases, increasing the degree of super cooling, can make phase γ nucleation and growth. Thus with the increase of B content, the content of γ phase gets less and the precipitation temperature gets lower. The precipitation of borides leads a lot Co, W solid solution, which made a growth of Al in the solid-liquid equilibrium phase and promotes the precipitation of Co3Al.