Abstract: Deflection in each optical path of binocular microscope system and unparallelism between them can increase the off-axis aberration, reduce the imaging quality, cause the nonidentity of binocular vision and lead to discomfort when used. A set of new method using laser is introduced to detect light path deflection and unparallelism. First of all, the system under test is divided into components and detected in each element, and then the parts are put together. A light path deflection distance more over than 0.5mm was detected in the experiment and a angle of about 0.8 was formed between the two outgoing beams after parallel light passing through the system. It is concluded that this method can be applied to industrial production and detection of microscope.