A method and apparatus are disclosed from the perspective of a User Equipment (UE) in a wireless communication system. The method can include receiving a configuration for a first set of power control information and a second set of power control information, receiving a Downlink Control Information (DCI) scheduling one or more Physical Uplink Shared Channels (PUSCHs), wherein the DCI comprises a first Sounding Reference Signal Resource Indicator (SRI) field and a second SRI field, determining a first Identifier (ID) directly based on value indicated by the first SRI field, wherein the first ID is a power control information ID in the first set of power control information, determining a second ID based on a value indicated by the second SRI field and the number of layers, and transmitting the one or more PUSCHs based on transmit power derived from the power control information of the first ID or the power control information of the second ID.