In satellite, the layout of the equipment is as possible as compact to reduce the cabin space. As a result, the electronic equipment, antennas, and cables are getting very close, causing the serious electromagnetic interference (EMI) issue. This paper investigates the mechanism of EMI between the automatic identification system (AIS) and the star sensor. A method is proposed to determine the noise interference source and the noise coupling path. The techniques to decrease the EMI due to the radiation coupling are developed. Experiments are conducted to validate the analysis and the proposed techniques.