The invention discloses a stress value calculation method of a pressure steel pipe in a hydraulic transition process. The method comprises the following steps: drawing a water flow characteristic curve based on the hydraulic transition process of a hydroelectric generating set, carrying out fluid mechanics calculation for calculating inner water flow of the steel pipe according to a hydraulic characteristic curve and a solid geometry model to obtain pressure distribution of the inner water flow of the inner steel pipe; carrying out flow-solid coupling analysis of the pressure steel pipe by considering the action of a water hammer on the steel pipe in the hydraulic transition process to obtain the stress distribution of the pipe wall of the steel pipe in the hydraulic transition process. The stress valve calculation method has universality and is capable of rapidly obtaining the stress distribution of the steel pipe and guiding the quality detection and the safety assessment of the stress steel pipe.