Abstract: The CubeSat has been developing rapidly due to the advantages of light weight, small size and high flexibility. In this paper, the three-unit CubeSat developed by Nanjing University of Science and Technology is studied. The finite element method is used to simulate its structure, which verifies that the modal frequency of the structure meets the rigidity requirement. Based on the simulation results, the PVC board is improved reasonably. The primary frequencies of the CubeSat in the three orthogonal directions are increased by 36.8%, 14.4% and 36.3%, respectively. At the same time, the vibration characteristics of the PVC board are improved. The research provides a basis for the vibration test and the structural design of other CubeSats.