The purple-black penis may be caused by excessive compression, penile incarceration, penile cancer and other factors. 1. Excessive pressure: excessive pressure on the penile area and long time of pressure may cause obstruction of blood circulation in the penile area, resulting in poor blood flow, which will make the penis purple and black. 2. Penile incarceration: if men have prepuce, forcible upturning of prepuce may cause penile incarceration, resulting in ischemia of the penile head, and ischemia for a long time may lead to penile purplish-blackness, which may be accompanied by pain, edema and other symptoms. 3. Penile cancer: it may be related to chronic inflammation stimulation, long-term smoking, sexual life chaos and other factors, in the early stage of lesion, there will be symptoms such as swelling and ulceration of penis, and with the aggravation of the lesion, necrosis may occur locally, which will lead to purple and black penis. To summarize, the penis purple and black, and accompanied by other abnormal manifestations, it is recommended that timely medical examination and treatment, to avoid the aggravation of the lesion.