The shock–boundary layer interaction mechanism of a transonic compressor profile at different Reynolds numbers (Re) was investigated by a three-dimensional Reynolds averaged Navier–Stokes simulation. The reason behind the deterioration of the transonic blade performance at low Re was revealed. Based on this, the mechanism of wall heat transfer regulating the interaction between the shock and the boundary layer on the blade surface was investigated to clarify the impact of wall heat transfer on transonic blade performance. The results show that as the Re decreases, the blade performance deteriorates, and a critical Re exists. When the Re exceeds this critical value, the separation structure on the suction side becomes the dominant factor contributing to losses. At this point, wall heat transfer reduces the gas kinematic viscosity near the wall, weakening the stabilizing effect of turbulence dissipation on the separated shear layer. This accelerates the transition process, consequently reducing the size of the separation bubble and decreasing blade losses. Below the critical Re, the passage normal shock approaches the exit of the blade passage and increases in strength, causing severe separation on the pressure side and resulting in a sharp decline in blade performance. At this stage, wall heat transfer can restore the blade’s boosting capability and weaken the passage normal shock. Although this may deteriorate the performance on the suction side to some extent, the degree of separation on the pressure side is significantly reduced, causing the wake region to narrow and improving blade performance. Comparatively, the control effect is more significant at a low Re (Re = 1.5 × 105), with losses reduced by 40.6 % compared to adiabatic wall conditions.