A method of single-cell point-to-multipoint (SCPTM) transmission for a mobile device in a wireless communication system is disclosed. The method comprises monitoring a message including mapping information between at least a temporary mobile group identity (TMGI) and at least a group radio network temporary identify (G-RNTI), determining whether a SCPTM service is started or activated according to whether one of the at least a TMGI corresponding to the SCPTM service is mapped to a G-RNTI, and performing a query procedure to start or turn on data transmission for the SCPTM service when the SCPTM service is not started or not activated.