To reveal the mechanism and evolution laws of the braking performance declining from heat load in the repeated braking applied for wet multidisc brake, a finite element analysis was carried out by using the bidirectional thermal-structure coupling method. Based on the fundamental principles of the energy conservation and virtual work principle, the elemental equations between temperature and heat load, and deformation displacement and load with heat transferring boundary conditions and heat–structure interaction were derived. Taking a steel disk in the brake for example, the deformation state of its elements, and the starting time, the location, the severity, and evolution laws of the plastic deformation were analyzed and demonstrated by using dimensionless stress distribution contours. The area in contact along the interface and the ratio of the element numbers to produce plastic deformation to the total element numbers on the steel disk were described by contact ratio and plasticity ratio, respectively. Moreover, the results under the repeated braking case were compared with that under the lasting braking case, which indicates that the influence of the temperature load on the performance declining of the repeated braking case is much lower than one of the lasting braking case, and the temperature is lower than 40 K and the plasticity ratio is smaller than 0.35 after the braking time is longer than 350 s. The conducted finite element analyses provided the theoretical fundamentals for the design and the application of the brake in the heavy type of trucks.