When a subscriber registered in a first wireless private network system moves to a service area of a second wireless private network system, the roaming service method and system of the wireless private network systems in a multi-zone updates HLR and VLR information of the second wireless private network system and synchronizes the updated information with HLRs and VLRs of other regional wireless private network systems so that the subscriber can be provided with in-plant wired/wireless services in any regional wireless private network systems. When the wireless terminal subscriber registered in the first wireless private network system moves through the wireless private network systems in the multi-zone, the wireless terminal subscriber can be automatically serviced from the wireless private network systems regardless of regions if the wireless terminal subscriber is located in any of the wireless private network system service areas.