A detection method for detecting quality of an optical element includes the following steps. Firstly, a point light source is provided. Then, the point light source is allowed to penetrate through the optical element, thereby forming a first optical image on an optical image processing device. Then, the position of the optical element is adjusted when there is a shade block included in the first optical image, and the point light source is allowed to penetrate through the optical element after the adjusting step, thereby forming a second optical image on the optical image processing device. Afterward, the first optical image is compared with the second optical image to discriminate whether the shade block is synchronously moved with position adjustment of the optical element so as to realize the quality of the optical element.