Protocol conversion is usually used to solve the problem of data interaction between different protocols, and its nature is to find mapping relationship between different protocol fields. In the traditional methods of protocol conversion, several drawbacks are identified: traditional conversions are mainly designed on the basis of specific protocols, so that they are static and lack flexibility, and are not suitable for environments with multi-protocol conversion; whenever a protocol changes, a reanalysis of the protocol’s structure and semantic fields is required to reconstruct the mapping relationship between fields, leading to an exponential increase in workload and a decrease in protocol conversion efficiency. Therefore, a general method of protocol conversion based on semantic similarity was proposed to enhance protocol conversion efficiency by exploring the relationship between fields intelligently. Firstly, the BERT (Bidirectional Encoder Representations from Transformers) model was employed to classify the protocol fields, and eliminate the fields that “should not” have mapping relationship. Secondly, the semantic similarities between fields were computed to reason the mapping relationship between fields, resulting in the formation of a field mapping table. Finally, a general framework for protocol conversion based on semantic similarity was introduced, and related protocols were defined for validation. Simulation results show that the precision of field classification of the proposed method reaches 94.44%; and the precision of mapping relationship identification of the proposed method reaches 90.70%, which is 13.93% higher than that of the method based on knowledge extraction. The above results verify that the proposed method is feasible, can identify the mapping relationships between different protocol fields quickly, and is suitable for scenarios with multi-protocol conversion in unmanned collaboration.