Method and apparatus of transmitting data duplication in a wireless communication system

A UE configured with data duplication comprising:

• a control circuit;
• a processor installed in the control circuit;
• a memory installed in the control circuit and coupled to the processor;
• wherein the processor is configured to execute a program code stored in the memory to:
• duplicate a data unit into a first data unit and a second data unit;
• construct a second Radio Link Control (RLC) Packet Data Unit (PDU) used for transmitting the second data unit, wherein the second data unit is a second RLC Service Data Unit (SDU);
• receive a control command from a network node, wherein the control command is used to deactivate the data duplication;
• and
• discard the second RLC PDU if the second RLC PDU includes the second RLC SDU.