A MVB network communication fault that occurred during the test run of Changsha maglev train was discussed , abnormal oscillation of the last MVB signal frame was found to be the direct reason. According to the theory of transmission lines, and combining with the analysis of oscillation phenomenon, this paper points out that the poor contact in the equipment of MVB network was the root cause. Through the theoretical formula and simulation modeling, the major factors that might cause a similar fault were researched, and the fault phenomenon was explained comprehensively. It also provides important reference value for the improvement of the EMC and reliability of train network communication system.