The spacecraft assembly mission cannot carry out effective Electromagnetic compatibility verification due to the constraints of large envelope of EMC test site, high test coverage and efficiency, and insufficient capability of dynamic condition verification. In order to solve the problem of simulation and verification of spacecraft assembly Electromagnetic compatibility, a combination-level evaluation method based on the prior data of electromagnetic radiation of modules is proposed in this paper, based on the electromagnetic field theory and Maxwell's equations derivation, the electromagnetic field radiated by a magnetic dipole at any point in space is obtained, and the electromagnetic radiation model of the component is reconstructed, to realize the prediction of electromagnetic radiation characteristics of composite body. The simulation results show that the proposed method can effectively support the prediction of electromagnetic radiation characteristics of cage-drawer integrated electronic equipment and spacecraft assembly.