A method is proposed for the fatigue strength testing of the underframe of a railway vehicle car body. Fatigue strength testing of individual components of the draft gear is conducted under laboratory conditions. Loads on individual components equivalent to vehicle loads are accurately determined in these experiments. The response of the tested specimen is consistent with the partial response of the entire car body. The basic process of reproducing the vehicle’s load spectrum on the simulation test platform is analyzed in detail. The vibrational state of the car body under realistic track conditions is accurately simulated on the test platform, which allows the body to be subjected to random loads and provides a basis for the specifications of follow-up fatigue tests on the car body and its components.