A storage device and a data storing method thereof are provided. The storage device includes a data storage medium and the control unit. The data storage medium includes a data storage area with a plurality of first type of data blocks. When a data reading operation is executed on a current data block of the data storage medium, the control unit determines whether a read count of the current data block is greater than a first threshold, determines whether the current data block is one of the first type of data blocks and generate a determination result according to the result, the control unit selects a plurality of first type of data blocks and switches the selected data blocks to a fast mode. Finally, the control unit moves data stored in the current data block to the selected data blocks under fast mode.