A method for performing adaptive locking range management, an associated data storage device and a controller thereof are provided. The method may include: receiving a security command from outside of the data storage device, wherein the security command is related to changing an old locking range into a new locking range; obtaining a start Logical Block Address (LBA) and a length value of the new locking range according to the security command; determining whether the start LBA of the new locking range is less than an end LBA of the old locking range, and determining whether an end LBA of the new locking range is greater than a start LBA of the old locking range; and in response to both determination results being true, performing data trimming on any respective non-overlapped portions of the new locking range and the old locking range.