A data storage device and a selecting bad data block method thereof which includes: writing data to a sample block; reading written data of the sample block as read data; comparing the read data and the written data of each data column in sample block, and calculating a number of error bits in each chunk accordingly; selecting a column with the largest number of error bits in a chunk with the largest number of error bits as a bad data column; and recording the sample block as a bad data block when determining that the number of error bits in the chunk is greater than or equal to the first threshold value and the number of bad columns in the chunk is greater than or equal to the second threshold value.