The invention relates to a method and a system for penetrating through a firewall based on the port forwarding multiplexing technology. The method comprises the steps of acquiring IP information of an internal network application end S and an external IP address of an external network control end C; forwarding and connecting through a data interface; monitoring the data interface; acquiring data of internal network application end S. With the adoption of the port forwarding multiplexing technology, the problem that the external network users cannot access the internal network application service protected by the firewall.