The invention relates to the field of automation of power system dispatching, and particularly relates to an illegal access detection method of a non-intrusive listening power dispatching service network. According to the method, an FPGA chip transmits listened data to an ARM processor through a PCI bus, the ARM processor analyzes and processes concurrence and sends an analysis result to an uppercomputer, a visible interface of the upper computer shows problem nodes in a graphical way so as to detect illegal access of the power dispatching service network. Compared with the prior art, the method has the advantages that the FPGA chip listens to the power dispatching service network in real time, the ARM processor performs high-speed analysis and alarm, a secondary device state model of thepower dispatching service network is built, and finally, captured nondestructive network communication is shown in a graph in a visible manner.