The invention relates to a method for determining the reliability of a system provided with a constant pressure element, belongs to the technical field of system reliability, and solves the technical problem that the function of the constant pressure element is ignored by an original GO method, and thus the determining precision of such system reliability is low. By adoption of the method provided by the invention, the determining precision of the reliability of the system provided with the constant pressure element can be improved; and the operator type is determined as 19A, thereby enhancing the function of the GO method, and expanding the scope of application of the GO method to determination of the reliability of the system provided with the constant pressure element.