Method and apparatus for time alignment regarding multi-TRP in a wireless communication system

A User Equipment (UE), comprising:

• a memory;
• and
• a processor operatively coupled to the memory, wherein the processor is configured to execute program code to:
• receive, from a network, a first signaling indicative of cell configuration of a cell, wherein the cell is associated with a first Timing Advance Group (TAG) and a second TAG, and the first signaling indicates an association between the first tag and a first Transmission Configuration Indication (TCI) state;
• receive, from the network, a second signaling indicative of switching a Special Cell (SpCell) of the UE to the cell, the first TCI state, and a first time alignment information, wherein the second signaling comprises at least a Medium Access Control (MAC) Control Element (CE);
• and
• in response to the second signaling indicating the switching, the first TCI state, and the first time alignment information:
• switch the SpCell of the UE to the cell or adding the cell as the serving cell;
• and
• apply the first time alignment information on the first TAG based on the association between the first TAG and the first TCI state in the first signaling.