A RACH-less HO method for a UE(120,420,1020) in a NTN system is provided, including: receiving a HO command from a source cell(411, 1011), wherein the HO command includes a RACH-less HO configuration and a RACH-based HO configuration associated with one of cells of the NTN system, wherein the RACH-less HO configuration includes a RACH-less available time and a UL transmission resource; determining a target cell(412,1012) according to the at least one cell configured by the HO command; performing a UL resource selection procedure to obtain a target UL transmission resource associated with the target cell(412,1012) for performing a target UL transmission to the target cell(412,1012); performing a HO confirmation procedure with the target cell(412,1012) by applying a UL timing adjustment information associated with the target UL transmission resource to perform the target UL transmission to the target cell(412,1012).