A data storage device including a flash memory and a controller. The flash memory includes a plurality of pages and a plurality of word lines, wherein each of the word lines controls at least two of the pages. The controller reads a first page of the pages in response to a read command, wherein the first page is controlled by a first word line of the word lines, and the controller further writes dummy data into the pages controlled by the first word line other than the first page when a predetermined condition is satisfied, wherein the predetermined condition includes that the first word line is not close.