A network switching method and a terminal device, which relate to the field of communications technologies, includes acquiring a network resource parameter of a network allowed to be accessed, and determining, from the network allowed to be accessed and according to the network resource parameter of the network allowed to be accessed, a target network to be switched to and a network resource parameter of the target network, where the network resource parameter of the target network is used to determine and set a running parameter of an application program that is to be run in the target network, and switching from a current network to the target network, and running the application program in the target network. The solutions can be used to enable the application program to implement, to some extent, seamless network switching.