The glans shows a dark purple color, then the possible causes: first, if there is a foreskin incarceration, or penile strangulation, then there will be ischemia of the glans and show a dark purple color. At this time will be accompanied by obvious pain, and there will be localized erosion or oozing and other changes, accompanied by swelling of the foreskin. Need to go to the hospital for further examination, if there is a foreskin inlay or strangulation, need to be manipulated to reset the treatment; second, if there is a long period of erection, such as abnormal penile erection lasts for more than half an hour without relief, there may be venous blood stagnation, which manifests itself as a dark purple glans, and at the same time there can be an abnormal erection of the glans; third, if the glans is infected, it can be manifested as a dark purple color. Acute phase infection, can be manifested as swelling obvious, accompanied by glans reddish color, accompanied by erosion and so on. With the gradual recovery of inflammation, the color can gradually show dark purple; fourth, for the circumcision or circumcision patients, the glans coronal region can show dark purple, not accompanied by any pain and swelling. Most of them are related to the glans being wrapped for a long time, local chronic hypoxic stimulation and other factors.