This paper studies several factors that affect the reliability of established structures .The theory of Data Mining is introduced into this paper as a new method to study the evaluation of established structures. New information is ultimately mined from “Data Sea” filed up in existed structures. According to the Chinese Structure Code and engineering experience, the factors affecting the reliability of structures are properly qualified as input parameters. This paper mainly researches with engineering structural examples on the theory of fuzzy cluster, which belong to the field of Data Mining. According to the analysis of the methods， it is found that the method put forward in this paper is practicable, reliable and effective.