The invention relates to a running-in test device for built-in axle boxes of a rail vehicle, comprising axle boxes and an axle passing through the axle boxes and further comprising a platform, supporting seats, axle box positioning seats, a driving unit, axle box temperature detection devices and a control device, wherein the supporting seats are fixedly installed on the platform, the axle box positioning seats are installed on the supporting seats, the axle boxes are fixed on the axle box positioning seats, one end of the axle is connected with the driving unit, and the driving unit and the axle box temperature detection devices are connected with the control device. The running-in test device has the advantages of simple structure, convenient operation and high degree of automation. Running-in test of built-in axle boxes of a rail vehicle after assembly is well implemented. The running-in test device can detect the temperature of bearings of the axle boxes in real time in the testing process, and the running-in test device automatically stops work and automatically records a running-in test result at the end of test.