In order to study the interaction between cracks, the thermal fatigue crack stress intensity factor of brake disc of high-speed train was calculated by the extended finite element method. The transient temperature field and stress field of the brake disc during braking were simulated by finite element software ABAQUS. Two groups of parallel cracks were placed in the highest temperature distribution area on the surface of the brake disc. Finally, the stress intensity factor of thermal fatigue cracks was calculated under the framework of online elastic fracture mechanics. The simulation results show that the peak temperature of the brake disc and the circumferential residual stress are 638.4℃ and 375.5 MPa under the first emergency braking mode with the initial speed of 400 km/h. The radial and circumferential distances of the cracks are very small, and the two crack tips are shielded. The shielding effect decreases with the increase of the spacing. The stress intensity factors at the tip of two dislocation parallel cracks increase with the increase of their radial distance in a small range.