A method and apparatus are disclosed from the perspective of a first network node. In one embodiment, the method includes the first network node transmitting a second transmission to a UE (User Equipment) in at least a first symbol of a first TTI (Transmission Time Interval). The method further includes the first network node transmitting a first transmission to a second network node in at least a second symbol of a second TTI, wherein the first TTI is TTI-level aligned to the second TTI and the first symbol is at least partially overlapped with the second symbol in time domain.