Abstract: In recent years, proprietary protocol has become an important form of standards in high-tech areas, such as the information and communication industry, which is profoundly changing the state of international standardization. With the case study of Cisco proprietary protocols, the formation mechanism of proprietary protocols is studied. The studies show that proprietary protocol resolves the contradictions between standard lagging and technology development. The leading enterprises establish installation bases by taking advantage of first-mover advantage. Then, due to the effect of path dependence and positive feedback, the proprietary protocol becomes the de facto standard by the interaction between proprietary protocol and leading enterprises.