A method for guaranteeing data not to be interrupted in a multi-network connection environment, applied between a user equipment, UE, connected with multiple networks and the multiple networks, comprising: when one or more network connections of the UE has congestion, a policy server transfers an IP flow of the UE to an uncongested network connection from the congested network connection(s), wherein that the one or more network connections of the UE has congestion is acquired by the policy server, when the policy server acquires that the one or more network connections of the UE has congestion, the step of transferring an IP flow of the UE to the uncongested network connection from the congested network connection(s) comprises: the policy server initiates to the UE a first IP flow transfer request to indicate the UE to transfer an IP flow of a designated service from a network connection of a source network to a network connection of a target network, wherein the source network is a congested network and the target network is a uncongested network; and the UE transfers the IP flow (202, 203) of the designated service from the network connection(s) of the source network to the network connection of the target network in response to the first IP flow transfer request; wherein the step of the policy server initiating to the UE the first IP flow transfer request comprises: the policy server inquires a preset connection policy, and selects as the designated service a service connected with the source network and required to be transferred according to the connection policy, and selects the target network, and initiates the IP flow transfer request to the UE; when acquiring that the source network is recovered to have normal network connection, the policy server inquires the preset connection policy, and initiates to the UE a second IP flow transfer request according to the connection policy to indicate the UE to transfer the IP flow of the designated service from the target network back to a network connection of the source network; and the UE transfers the IP flow of the designated service back to the network connection of the source network, in response to the second IP flow transfer request. the policy server initiates to the UE a first IP flow transfer request to indicate the UE to transfer an IP flow of a designated service from a network connection of a source network to a network connection of a target network, wherein the source network is a congested network and the target network is a uncongested network; and the UE transfers the IP flow (202, 203) of the designated service from the network connection(s) of the source network to the network connection of the target network in response to the first IP flow transfer request; wherein the step of the policy server initiating to the UE the first IP flow transfer request comprises: the policy server inquires a preset connection policy, and selects as the designated service a service connected with the source network and required to be transferred according to the connection policy, and selects the target network, and initiates the IP flow transfer request to the UE; when acquiring that the source network is recovered to have normal network connection, the policy server inquires the preset connection policy, and initiates to the UE a second IP flow transfer request according to the connection policy to indicate the UE to transfer the IP flow of the designated service from the target network back to a network connection of the source network; and the UE transfers the IP flow of the designated service back to the network connection of the source network, in response to the second IP flow transfer request. the policy server inquires a preset connection policy, and selects as the designated service a service connected with the source network and required to be transferred according to the connection policy, and selects the target network, and initiates the IP flow transfer request to the UE; when acquiring that the source network is recovered to have normal network connection, the policy server inquires the preset connection policy, and initiates to the UE a second IP flow transfer request according to the connection policy to indicate the UE to transfer the IP flow of the designated service from the target network back to a network connection of the source network; and the UE transfers the IP flow of the designated service back to the network connection of the source network, in response to the second IP flow transfer request.