Super304H austenitic stainless steel has been widely used in superheater and reheater pipes of the ultra-supercritical thermal power unit boilers. During long-term thermal exposure, reheat cracking is prone to occur at the assembly of the pipeline weld joint. This study systematically studied the effect of temperature on the reheat cracking susceptibility of Super304H austenitic stainless steel weld metal by a pre-compressed CT specimen method. The results show that the time required for the weld metal to generate cracks at 650 ℃ is shorter than that of the weld metal at 600 ℃, leading to a higher reheat cracking susceptibility. The main reason for this phenomenon is that the grain boundary strength decays faster with time and the higher stress relaxation rate at 650 ℃, while the influence of intragranular strengthening difference at different temperatures is negligible.