The invention discloses a heat treatment process of an oval end socket forged piece for a nuclear power evaporator. The heat treatment process is used for heat treatment on the oval end socket forged piece made of SA508Gr.3Cr.2 steel with the outer diameter size Phi being larger than or equal to 6000 mm. The heat treatment process includes the following steps that (1), a forged piece is heated to 720-810 DEG C in a heating furnace, and heat preservation is performed; and water-cooling quenching is performed after heat preservation is performed; (2), the forged piece is heated to 880-900 DEG C in the heating furnace, and heat preservation is performed; and water-cooling quenching is performed after heat preservation is performed; (3), the forged piece is heated to 635-655 DEG C in the heating furnace, and heat preservation is performed; and the forged piece is subjected to air cooling after heat preservation is ended. After treatment of the heat treatment process, the end socket bowl end and the boss position of the oval end socket forged piece both obtain seventh-grade granularity, compared with a conventional process which obtains sixth-grade granularity, the granularity is increased by one grade, the overall toughness of the forged piece is also greatly improved, a large surplus is obtained compared with performance assessment requirements , and the risk of unqualified products can be lowered.