Abstract: Drivers always determine whether there is a foreign object between the door and the platform screen door(PSD) through checking the light bar’s completeness in the rear of the subway at Chinese subway. However, there is a big risk of false positives. Based on the characteristics of the gap between the subway door and PSD, the article made a detailed comparison of different foreign object automatic detection from the system performance, installation and maintenance, etc., proposed self-detection method based on machine vision between PSD and the door foreign object. Experimental results showed that the method was with the properties of high detection rate, the equipment was small, simple for installation and maintenance, and low cost.