The invention discloses a public network and private network self-adapting method and device. The method comprises the steps of when a private network is congested, selected part of terminals is disconnected; a private network broadcast identifier is modified and private network access forbidding information is set in the broadcast identifier; the public network sends a load search request to the private network according to a preset cycle; the private network receives the load search request, searches network load and judges whether the network load is smaller than a preset load threshold value or not; if the network load is smaller than the preset load threshold value, a congestion removal instruction is fed back to the public network, the private network broadcast identifier is modified and private network access allowed information is set in the broadcast identifier; and the public network receives the congestion removal instruction sent by the private network, disconnects connected terminals according to the information in the congestion removal instruction and enables the terminals to be connected with the private network again. According to the public network and private network self-adapting method and device, the congestion problem of the public network can be effectively solved, and when the congestion of the private network is removed, the terminals in the public network can return to the private network.