In order to analyze the discrete characteristics of the vibration source of subway trains and the dominating factors in different frequency bands, two sections in the same part of a subway line are tested in situ. The whole-day test samples are statistically analyzed from time domain and frequency domain. The results show that the vibration source intensity of the test section has a dispersion of more than 15dB, and presents periodicity related to train formation: the vibration source intensity does not increase significantly during the morning and evening peak hours; the vibration response difference caused by the same train passing through the fixed test section multiple times, mainly affected by the discreteness of the frequency band below 6.3 Hz; this frequency band is mainly derived from the quasi-static excitation of the train, and is directly related to the load of the train: the vibration response in the 8~250 Hz frequency band between different trains is dominated by the difference of the wheel out-of-roundness state; the maximum difference of the frequency division vibration acceleration level in this frequency band is close to 20dB, which directly leads to the significant dispersion of the measured vibration source intensity samples throughout the day.