Abstract:The vibrations of subgrade in the Qinhuangdao—Shenyang rail line are tested by ambient excitation and train loads excitation. The frequency of the trains load,the nature frequency,and vibration frequency of subgrade under trains load are obtained through frequency spectrum analysis. The frequency structure of the subgrade and the relationship between the vibration acceleration and train speed are analyzed. The results show that vibrations of the subgrade have close relation with the nature frequency of the subgrade and train velocities. It is also shown that,at a certain train velocity,the vibration acceleration will reach to maximum value.