Abstract: A cooling method of a hydrotreating plant having a desulfurization section (1) including a furnace (12) for heating liquid to be processed, reactors (14, 15) for hydrotreating sulfur to generate hydrogen sulfide, a hydrogen sulfide absorber (19) for absorbing the hydrogen sulfide generated in the reactors (14, 15), and a compressor (21) for compressing and transferring fluid from the hydrogen sulfide absorber (19) toward the reactors (14, 15), the cooling method comprising the steps of gradually depressurizing the hydrotreating plant at the desulfurization section (1) to a pressure level at which reactor material does not embrittle and gas does not leak due to difference of mechanical thermal expansion in the plant after stopping supply of the liquid to be processed, operating the compressor (21) approximately at the maximum rotation number, and completely extinguishing burners (12A, 12B) in the furnace (12) during plant shutdown operation.