A method of detecting a bad servo track of an HDD includes measuring servo AGC of each of servo sectors of a servo track requiring determination of badness, calculating statistic data with respect to the measured servo AGC of each servo sector, and determining whether the servo track is bad based on the calculated statistic data. Since the badness of a servo track is determined based on the statistic data of the servo AGC, a bad servo track generated due to a change in the overall magnitude of a servo signal is easily detected so that reliability in the detection of a detective servo track can be improved.