A method and apparatus are disclosed from the perspective of a network. In one embodiment, the method includes the network configuring a DL (Downlink) BWP (Bandwidth Part) and an UL (Uplink) BWP in a first serving cell to a UE (User Equipment). The method also includes the network configuring a paired spectrum operation in the first serving cell to the UE. The method further includes the network transmitting a first DCI (Downlink Control Information) to the UE, wherein the first DCI comprises a slot format combination indicating one or more slot format values for the DL BWP and one or more slot format values for the UL BWP. In addition, the method includes the network prevents from setting an amount of slot format values in the slot format combination in the first DCI to be not divided by a first number, wherein the first number is associated with an absolute value of a difference of a first SCS (Subcarrier Spacing) configuration and a second SCS configuration.