To realize the fusion application of multi-source data, online detection devices with different data exchange protocols need to be connected to the intelligent operation and maintenance diagnosis platform of a substation. In response to this need, an intelligent protocol conversion method with the functions of automatically identifying the protocol used in the other side of communication and adaptively configuring the parameters of the interconversion protocols is proposed. By judging multiple special fields of the data frame, the data exchange protocol followed by the data message is preliminarily determined. The data exchange protocol followed by the other side of communication is finally determined by tentatively testing the command type field and the check code field of the data frame. Through the conversion mode of "communication message A-database-communication message B", the protocol conversion modes of "one-to-many", "many-to-one" and "many-to-many" are realized. An implementation scheme, and its technical details, of the proposed intelligent protocol conversion method are introduced in detail. The proposed method makes up for the deficiency of the traditional "one to one" protocol converter and provides a convenient method for all kinds of online detection devices to access the intelligent operation and maintenance diagnosis platform of a substation. This work is supported by the National Key Research and Development Program of China (No. 2017YFB0902800) and the Science and Technology Project of State Grid Corporation of China (No. 52094017003D).