A method for network function customization performed by a system comprising a first network controller in a current network and a second network controller in a target network, wherein the method comprises: • obtaining, by the first network controller, target network information of the target network that is to be accessed by an access terminal, wherein the target network information contains a standard of the target network and a bandwidth of the target network; • obtaining, by the first network controller, information about the current network used by the access terminal and user data access frequency information, wherein the user data access frequency information includes private data access frequency information and user customized service access frequency information, wherein the private data access frequency information is access frequency information about user private data not stored in the access terminal and the user customized service access frequency information is access frequency information about a user customized service, wherein the information about the current network contains a standard of the current network; • obtaining, by the first network controller, according to the standard of the current network and the standard of the target network, a network standard available to the access terminal in the target network and needed by the access terminal when the access terminal accesses the target network, obtaining, by the first network controller, according to the user data access frequency information, user data that is needed by the access terminal when the access terminal accesses the target network, wherein the user data is at least one of user private video information, user private image information and user private text information, obtaining, by the first network controller, according to the obtained available network standard, the bandwidth of the target network and the user customized service access frequency information, a network customized service, wherein the network customized service is a service whose user customized service access frequency is greater than a threshold, • transmitting, by the first network controller, before the access terminal moves into the target network, the user data and information indicating the network customized service to the second network controller; • receiving, by the second network controller, the user data and the information indicating the network customized service; • preparing, by the second network controller, network resources for the access terminal according to the user data and the information indicating the network customized service. • obtaining, by the first network controller, target network information of the target network that is to be accessed by an access terminal, wherein the target network information contains a standard of the target network and a bandwidth of the target network; • obtaining, by the first network controller, information about the current network used by the access terminal and user data access frequency information, wherein the user data access frequency information includes private data access frequency information and user customized service access frequency information, wherein the private data access frequency information is access frequency information about user private data not stored in the access terminal and the user customized service access frequency information is access frequency information about a user customized service, wherein the information about the current network contains a standard of the current network; • obtaining, by the first network controller, according to the standard of the current network and the standard of the target network, a network standard available to the access terminal in the target network and needed by the access terminal when the access terminal accesses the target network, obtaining, by the first network controller, according to the user data access frequency information, user data that is needed by the access terminal when the access terminal accesses the target network, wherein the user data is at least one of user private video information, user private image information and user private text information, obtaining, by the first network controller, according to the obtained available network standard, the bandwidth of the target network and the user customized service access frequency information, a network customized service, wherein the network customized service is a service whose user customized service access frequency is greater than a threshold, • transmitting, by the first network controller, before the access terminal moves into the target network, the user data and information indicating the network customized service to the second network controller; • receiving, by the second network controller, the user data and the information indicating the network customized service; • preparing, by the second network controller, network resources for the access terminal according to the user data and the information indicating the network customized service.