An optical disk differentiating method applied to an optical disk drive, in which a first level value, a second level value and an optical disk differentiating value generating program are stored and an optical disk is put. The method comprises the steps of: generating a laser beam impinging on the optical disk; generating a first reflex signal when the laser beam is reflected by a surface of the optical disk; generating a second reflex signal when the laser beam is reflected by a reflex layer of the optical disk; calculating a first time frame value when the first reflex signal is greater than or equal to the first level value, and rendering a first beginning time value when the first reflex signal firstly equals the first level value; enabling the optical drive to obtain an optical disk differentiating value according to the first time frame value and the optical disk differentiating value generating program; calculating a second beginning time value as the second reflex signal firstly equals the second level value; calculating a difference between the second beginning time value and the first beginning time value and defining the difference as a response time value; and comparing the response time value with the optical disk differentiating value to determine a type of the optical disk.