Abstract: In order to satisfy the demand of megawatt-class and lightweight for future deep space exploration,the Institute of Nuclear Energy Safety Technology proposed the preliminary design for a 5.2 MWt space lithium-cooled nuclear reactor. The reactor design has many unique features,such as the integrated fuel,the non-uniform lithium flow channels,and the control system consisting of boron powder and control rods that can compensate reactivity by emptying the boron powder with the reactor operation. For a new type of space nuclear reactor design like this,there is little design experience. The preliminary design of the reactor needs to be verified and optimized with high fidelity simulation,which can be carried out with the coupled Monte Carlo and computational fluid dynamic（sCFD）simulation. In this contribution,the coupling neutronics and thermal performance of the reactor design was evaluated. The coupling results show that the reactivity requirements of the reactor design can be satisfied. The non-uniform flow channels flatten the power distribution,and the temperature of each material is lower than the limit under normal operating condition. The design of the model basically meets the requirements,and the coupling results also provide optimization ideas for the design.