The traditional automatic restoration technology for proprietary protocol needs to master the prior knowledge in advance and set the parameters. It is difficult to obtain scientific and reasonable parameter configuration results, which leads to great differences between the restored proprietary protocol and the original proprietary protocol. To this end, a new automatic protocol automatic reduction technology for large-scale power industrial control systems is proposed. The proprietary protocol of large power industrial control system is described by a finite state machine. In the process of parsing the proprietary protocol, the reference model is parsed upwards from the bottom layer, and the proprietary protocol is divided into different hierarchical protocols through the tree structure. Different parts are displayed, and a detailed analysis process is given. According to the Lua script specification, the design of the proprietary protocol script code is completed through proprietary protocol registration, proprietary protocol resolution, and proprietary protocol submission. The proprietary protocol parsing is a key part, which is completed by calling the corresponding interface function and the parser interface function of proprietary protocol. The parser uses the method of providing the private interface to call the plugin to develop the parsing protocol, and the compiled library file is added in the established source code directory. The causal segmentation reconstruction method is used to calculate the $\boldsymbol{\varepsilon}$ machine of the proprietary protocol, and the proprietary protocol is automatically restored. The experimental results show that the proposed method has good effect on the analysis and restoration of the proprietary protocol and is highly practical.