Abstract: The space technology has greatly potential and important implication for the country’s science, national defense, politics, and economy. To minimize loss in launch and operation, the quality optimization was discussed as an important project in the study of space nuclear reactors. The structure design and optimal parameter design were studied to meet the requirement of space condition and launch condition. The space reactor type and structural plan design were proposed based on research on kinds of space nuclear reactor designs oversea. The engineering design optimization was transformed into the solving of a nonlinear integer optimization through mathematical modeling, and optimal parameter of the model was obtained in theory by Matlab programming method. The optimization problem was solved by mathematical software, and the important influencing design variables including the quantity of control drum and the radius of reactor core were discussed. The result shows that the total mass of space reactor body decreases by 14.3% compared with the original model, and the study can improve the further more complicate space nuclear reactor design research.