A packet transmission method is disclosed herein. The packet transmission method includes the following operations. The first packet is transmitted to a first proxy server terminal by a first user terminal. A header of received first packet is changed to generate a first header, and the first packet with the first header is transmitted to a gateway terminal by the first proxy server terminal. The first header of the received first packet is changed to generate a second header, and the first packet with the second header is transmitted to a server terminal by the gateway terminal. The header of the first packet includes a source address field and a destination address field.