The invention discloses a vascular dermatosis detecting and positioning device. A sample arm comprises a probe outer shell, a handle, a collimator, a scanning galvanometer, a galvanometer support anda lens and is characterized in that the lens is mounted on a threaded lens holder in threaded connection with the probe outer shell; a light-permeable sheet is mounted on a support which is arranged on one side, with the lens, of the probe outer shell, and a light path passes through the lens and the light-permeable sheet. A system comprises the sample arm, a wide-angle camera, a reference arm, a10:90 coupler, a circulator, a spectrograph, a computer, an infrared broadband light source and a red light source. In OCT-A vascular dermatosis clinical detection, uniformity of scanning positions before and after surgeries is realized, high stability in detection is realized, and debugging time in detection is shortened. In addition, stability and convenience in a vascular dermatosis detecting process are greatly improved.