A method for calibrating a relative tilt angle between a disc and a pickup head using a focus signal. The method includes the steps of moving the pickup head to a first position and performing the focusing operation; obtaining a first variation of a focus signal of the pickup head at a first position; moving the pickup head by a default distance to a second position and performing the focusing operation; obtaining a second variation of the focus signal of the pickup head at a second position; and calculating the relative tilt angle according to the default distance and the first and second variations. The focus signal includes a focus error signal and a focus control signal, both of which have been stored in a control circuit of an optical disc drive. Consequently, the invention utilizes the focus signal to detect the tilt angle of the pickup head without adding any displacement sensor.