The invention discloses a method for realizing a user-defined proxy tunnel protocol based on a SNI mechanism of a TLS protocol, the method comprises the following steps: 1) a client side sends a handshake request to a proxy server side to request a SSL for handshake, and indicates a true server address and a protocol type through a server extension; 2) the proxy server side analyzes the server extension and detects a type of an analysis result, if the detected type meets requirement, a connection between the proxy server side and the client side is marked, and the analysis result is stored; 3)the client side initiates a HTTP service request to the proxy server side; 4) the proxy server side detects whether the connection where the HTTP service request is has a mark, if so, the proxy server side modifies an access target, splices the analysis result with a currently requested path address to obtain a true service address. The method provided by the invention realizes that a problem ofcomplexity in the protocol caused by the original user-defined tunnel protocol is solved based on the SNI mechanism of the TLS protocol.