A packet transmission method and an apparatus pertain to the field of network technologies. The method includes obtaining, by a terminal device, a source IP (Internet Protocol) address in a to-be-transmitted packet and N IP addresses of the terminal device, where N is an integer, and when the source IP address in the to-be-transmitted packet is different from any one of the N IP addresses of the terminal device, determining that the source IP address in the to-be-transmitted packet is forged, and prohibiting transmitting the to-be-transmitted packet. The application can solve the problem that a virus such as Trojan in the terminal device may be prevented from forging a source IP address of another device to randomly transfer an attack packet in the network to improve network security.