The invention discloses a post-forging heat treatment method for ultra-supercritical turbine blade steel and belongs to the field of steel heat treatment. The post-forging heat treatment method comprises the following steps that firstly, homogenizing treatment is conducted; secondly, fast cooling is conducted till the nose tip temperature of a C curve, so that structure transformation is conducted; thirdly, cooling is conducted to the temperature below the Ms point, and structure transformation is further conducted; fourthly, heating is conducted to a certain temperature, heat insulation is conducted, and a base body is subjected to desolvation and softening; and fifthly, speed-limiting furnace cooling is conducted till the steel is discharged out of a furnace. According to the method, heat treatment is directly conducted after forging, the forging stress is eliminated, the steel structure is homogenized, mixed crystals are reduced, sufficient preparation is made for subsequent quenching and tempering treatment, and therefore the performance obtained after quenching and tempering is effectively improved, especially the impact performance of the steel is improved, and the impact is improved to 54 J or above from the value about KV2 16 J of a traditional technology.