A data storage device with improved space-trimming capability. A microcontroller operating in accordance with a host allocates a non-volatile memory to store data. The microcontroller manages the mapping information between the logical addresses used by the host and the space of the non-volatile memory. The microcontroller further takes responsibility for the transformation of a trimming command that is issued by the host to invoke a plurality of trimming requests. After the transformation, a target-host block repeatedly indicated by the plurality of trimming requests is transformed to be trimmed at one time. The mapping information of the target-host block, therefore, is not read frequently from the non-volatile memory for real-time amendment.