Continuous synchronous encryption and decryption in a wireless communications system throughout handoffs.

Comprising a group of fixing service device and portable communication device in a wireless communication system, each comprising an encryption synchronous counter, the portable communication device and fixing service unit comprises a data transmission format; and ring-shaped zone switching time with a synchronously method, comprising the following steps: (a) during handover preset, loads to the casing value and a content of the second fixing service device for encrypting synchronous counter; (b) is continuing the switch value increase the second fixing service device for encrypting synchronous counter and portable communication device for encrypting synchronous counter the ring-shaped zone handover alarm time synchronously.