The invention discloses an industrial control system access control method based on an OPC protocol. The method comprises the steps that a port number whitelist is established; S2, OPC message data are acquired and whether the OPC message data are a server request message or a response message is judged; S3, the client side port number transmitting the message data is acquired and matched with the client side port number in the whitelist; S4, the OPC message fields of the client side are detected; and S5, the process ends. According to the security gateway protection system access control method based on the OPC protocol, the requirements of security protection of an industrial control system and the overall security protection of enterprise network interconnection thereof can be met.