Reliability analysis of structures containing defects carried out directly by practising engineers is quite complex and costly. Therefore. a simple and convenient reliability analysis method should be investigated and established. In this paper. the principle and building procedure of a reliabjlity analysis method are described and the feasibility of the method are also explicitly clarified. Based on the assumptions that: (1) the 1oad is a deterministic variable; (2) the yield strength and fracture toughness sarisfy normal distribution and their variational coecients are constant; (3) the initial crack length remains unchangeable, a set of probabilistic failure assessment diagrams (PFAD) called elementary reliability assessment method are established under the simplified option 1 curve of the 3rd version of CEGB R6. The investigation shows that the distribution of random safety factor and failure probability of a structure only depend on the Coordinates of the expectation of P (Lr, Kr) in the failure assessment diagram of the simplified option l curve and is not influenced by the other factors. The investigation further shows that the failure probability will decrease with the increase ofthe initial crack length if the expectation of P (Lr, Kr) keeps unchanged. A conservative result will be given when using the PFAD as an elementary reliability analysis method to assess the integrity of a structure and only a simple procedure is required Jike the deterministic assessment method given in CEGB R6. When the secondary stress exists. the conservativeness of the result assessed will increase with the increase of parameter P although the PFAD is only established based on considering primary stress.