A circuit for calibrating a focus position of an optical module includes a calibration signal generating unit and a focus position adjusting unit. The calibration signal generating unit is utilized for generating a calibration signal according to a first focus signal and a second focus signal at the same time, where the first focus signal and second focus signal correspond to a first focus position and a second focus position, respectively, and the first focus position is different from the second focus position. The focus position adjusting unit is coupled to the calibration signal generating unit and is utilized for adjusting the focus position of the optical module to a specific focus position according to the calibration signal.