A method for screening bad columns in a data storage medium includes steps of: writing predetermined data into at least one sample block; comparing the written data with the predetermined data to calculate numbers of error bits in the plurality of columns; defining an inspection window covering a portion of the columns; summing the numbers of error bits in the portion of columns in the inspection window to obtain a total number of error bits and determining whether the total number of error bits is greater than a number of correctable bits; if yes, determining a start point and a terminal point of a bad column interval in the inspection window, wherein the numbers of error bits in the columns between the start point and the terminal point are greater than a threshold of error bits; and labeling the columns in the bad column interval as bad columns.