Existing researches on the crack propagation mechanisms in composite pavement often focus on materials, but do not emphasize structure. There are many simulation methods, but they are difficult to reflect actual working conditions. To solve these problems, this study conducts an in-depth investigation on the fatigue crack propagation behavior of non-linear damage in composite pavements. Using damage mechanics theory, residual strength theory, accelerated loading tests, and Python algorithms, a comprehensive simulation of the mechanical behavior of cement concrete slab joint load transfer was conducted. A cycle fatigue damage-fracture simulation system was established using the DLOAD subroutine, UMAT subroutine, UDMGINI subroutine, and XFEM main program. This system reveals the degradation patterns 4 key indexes under cyclic loading: reflection crack propagation rate, internal material damage, residual strength, and pavement deflection. The results show that fatigue damage accumulates with the increase of loading cycles, leading to a gradual decline in residual strength, with the damage accumulation rate closely linked to the extent of residual strength reduction. Under axle loads of 100 kN, 160 kN, and 220 kN, the crack propagation phase accounts for 43.94%, 35.34%, and 28.82% of the pavement’s full life cycle, respectively. For vehicle speeds of 40 km/h, 60 km/h, and 100 km/h, the crack propagation phase comprises 46.83%, 43.94%, and 43.13% of the pavement’s life cycle, respectively. Overloading significantly impacts pavement stability, accelerating fatigue damage and reducing service life.