A method and system for maintaining uplink synchronization in CDMA based mobile communication system with high accuracy and fast update frequency, said mobile communication system comprising a base station, at least one mobile station, said method comprising the steps of: receiving signals transmitted by one of said mobile stations; measuring timing of the transmitted signals from the mobile station and obtaining USActual value currently used in the mobile station; calculating a USTarget value based on the measurement; comparing USActual and USTarget to generate a SS command for increasing or decreasing said USActual; signaling said synchronization shift (SS) command in downlink to said mobile station to increase or decrease said USActual.