This research is based on the project investigation and repeated discussion. The British standard BS7910 was the basic theory, and accordingly carried out the experiment, the computation of the stress parameter and an expert system was developed. In this research, the test materials were gathered from project location, and uniaxial tension test, fracture toughness test are made. Then a material parameter database was established; in the research process, the FEA models of typical power plant pressure vessel were established and the stress parameters were gained through simulation method, and a classified stress database was established. The expert system is an effective assistance method for the safety assessment of the flaws, and it may help the ordinary engineers and technicians to grasp the complex assessment process.