In this paper, a simplified fault diagnosis method based on Petri nets is proposed to estimate the faulty item/section(s) of a large power generation station. The Petri nets are used as a modeling tool to build fault diagnosis models of item/section(s) of power station which aim to diagnose accurately the faults when a large amount information of SCADA system is detected in the control room. It can diagnose and estimate the faulty item/section(s) correctly for multiple faults as well as simple faults. In order to testify the validity and feasibility of that method, a computer simulation of High Dam power generation station is used. It is shown from three study cases that Petri nets fault diagnosis method has many merits such as accurate fault diagnosis results, easy and flexible correctness of Petri net fault diagnosis models for each item/section(s).