Aiming at analyzing the looseness of skirt lock during operation,lateral vibration test was carried out. The effects of initial preload,transverse cyclic excitation ’s amplitude,removal times and thread type were investigated. The finite element simulation analysis was carried out to verify the effectiveness of the results. The test results show that the larger the initial preload and the smaller the amplitude,the less the skirt lock loosens. The removal times have no effect on the skirt lock loosens. Under the same conditions,the ordinary thread is more difficult to loosen than the trapezoidal thread. But because of the working nature of the skirt lock,the trapezoidal thread is selected. The research results are significance to the analysis of the causes of the looseness of the skirt lock and the design of anti loosing.