The present invention relates to a vertical hand-off (Vertical Handoff) method. According to the present invention, heterogeneous (heterogeneous) determines the serving network of the possible terminal connected to the second network in the service coverage area overlap between the network service coverage is relatively narrow and wide first network. If the serving network is the first network, it determines whether the second signal strength (received rignal rtrenth, rss) is more than a first threshold value that is received from the network. And using the results of the first prediction variation pattern of the threshold value or greater signal strength to determine whether the first vertical handoff. If the serving network is the second network, the second signal strength received from the network determines whether the second threshold value or less. And using the results of the prediction less than the second threshold value variation pattern of the signal strength to determine whether the second vertical handoff. In this case, the first threshold value is characterized by having a value greater than the second threshold value. Vertical handoff ping-pong effect, the received signal strength, RSS, threshold