A method and apparatus are disclosed from the perspective of a UE (User Equipment). In one embodiment, the method includes the UE being configured with a control resource set (CORESET). The method further includes the UE receiving a Downlink Control Information (DCI) on the CORESET, wherein an index is included in the DCI and the index indicates a time domain resource allocation pattern. The method also includes the UE receiving data in Orthogonal Frequency Division Multiplexing (OFDM) symbols determined according to the time domain resource allocation pattern, wherein a range of the time domain resource allocation pattern starts from the first OFDM symbol of the CORESET or after an offset from the first OFDM symbol of the CORESET, and the range of the time domain resource allocation pattern may end across a slot boundary.