1. A defocus calibration module, applied in a light-sensing system, the light-sensing system being utilized for sensing a measured object for generating a sensed image, the light-sensing system having a light-emitting component, a focusing component, and an image sensor, the light-emitting component emitting a detecting light to the measured object so that the measured object accordingly generates a reflecting light, the focusing component being utilized for focusing the reflecting light to the image sensor, the image sensor being utilized for generating the sensed image according to the reflecting light, the defocus calibration module being utilized for calibrating the sensed image, the defocus calibration module comprising: a calibrating object, located between the measured object and the focusing component, for blocking a part of the detecting light and a part of the reflecting light for forming images respectively at a first calibration imaging location and a second calibration imaging location in the sensed image; and a calculating circuit, for calibrating the sensed image according to the first calibration imaging location and the second calibration imaging location, wherein the calculating circuit calculates a defocus parameter of the light-sensing system according to the first calibration imaging location, the second calibration imaging location, and a predetermined incidence angle of the detecting light, and calculates an original image of the measured object according to the defocus parameter and the sensed image; wherein the defocus parameter represents a sum of an object-distance error and an image-distance error; wherein the object-distance error is a difference between a length of a distance, which is between the measured object and the focusing component, and a length of a front focal distance of the focusing component; wherein the image-distance error is a difference between a length of a distance, which is between the image sensor and the focusing component, and a length of a back focal distance of the focusing component.