The invention discloses a data transmission method and system based on dynamic port switching. The method comprises the following steps that: a transmitting end and a receiving end establish a connection including a first source port, and the transmitting end sets a second source port; the transmitting end transmits a message to the receiving end through the first source port; and the transmitting end establishes a connection with the second source port and transmits the message when the connection between the transmitting end and the receiving end is disabled. In the data transmission method and system, an automatic 'connection disabling' detection mechanism and a dynamic port switching mechanism are adopted, so that the problem of limitation on connections by transmission link infrastructure can be solved effectively by the dynamic port switching mechanism; automatic reconnection after disconnection on the aspect of transmission protocol is realized; and data transmission stability is ensured. The data transmission method and system are completely transparent to an application layer.