The present invention provides a method for a communication terminal to reside in a plurality of networks, and a communication terminal thereof. The method comprises the steps of: acquiring a first signal intensity corresponding to a first communication network and acquiring a second signal intensity corresponding to a second communication network; when the first signal intensity is greater than a first threshold, registering a first service in the first communication network; when the second signal intensity is greater than a second threshold, registering a second service in the second communication network; when the second signal intensity is less than or equal to the second threshold, searching for the second communication network and registering the second service in the first communication network; and when the first signal intensity is less than or equal to the first threshold, searching for the first communication network and registering the first service in the second communication network. According to the present invention, the communication terminal can operate at both the first communication network and the second communication network simultaneously, and can execute the first service and second service at the same time. As a result, it is able to ensure a normal, basic communication service as well as a high-speed data service.