Trackless trains adopt public right-of-way. The braking distance requirements are strict, and large deceleration is required to stop the train. Brake disc is an important part of the trackless train, its service performance directly affects the braking safety of the train, and the temperature and stress are the key performance parameters. In order to investigate the influence law of variable working conditions on the temperature and stress of the brake disc, for the problem that it is difficult to simulate the extreme working conditions based on the real measurement method, the brake disc of a 3-vehicle and 6-axle trackless train is taken as the research object. According to the structural dimensions and material parameters, a thermo-mechanical coupling simulation model of the brake disc is established based on the theories of transient thermodynamics and heat transfer. Based on the standard comparison analysis, the deceleration index of the trackless train to meet the requirements of braking distance is designed, and the virtual test of the temperature and stress field of the brake disc is carried out under the conditions of different loads, deceleration, and ramp gradient. The results show that it is feasible to simulate the extreme working conditions based on the virtual test, and the maximum temperature and stress of the brake disc increase with the increase of load, deceleration and ramp gradient. Under the extreme working conditions, the maximum temperature of the brake disc is about 680.4 ℃, and the maximum stress is about 1240 MPa. The research results provide a reference for the safe operation and maintenance of the trackless train.