Abstract: Aimed at the problem of adjacent frequency jam caused by 4G system on Radio Determination Satellite Service (RDSS) of Beidou system, the analysis way based on the decomposition of wholemachine module is proposed. The main technical measures of restraining from outofband jam are summarized theoretically. Effective bandwidth and processing gain are two key indexes, and the main module is Radio Frequency (RF) module. According to the results of theory analysis, the different RF channels of different apparatus parameters are designed, and the outofband rejection ability of each RF channel is verified on the united test platform. The law and otherness of the test results are described. The research results can provide technical foundation for the compatible coexistence of Beidou system and 4G system.