In order to confirm danger and security degree of pressure vessel, fuzzy assessment was put forward. Aimed to plastic collapse and fracture assessment of a plane defect of pressure vessel, the least distance ,between assessment dot and failure assessment curve (FAC), was translated into fuzzy degree gene. According to membership grade of the fuzzy assessment, fuzzy assessment model was established, and could be used to confirm the plane defect degree of danger and security. The whole vessel’s defects degree of danger and security were given by an integrated method. The method is intuitionistic, exact and reliable, and also could be applied to other analogous systems.
