The possible causes of thick penile blood vessels are physiological factors, congenital dysplasia, local varicose veins of the penis and so on. 1. Physiological factors: when the penis is in an erect state, the corpus cavernosum will be congested with blood, and the blood vessels in the congested state of the penis will appear thick. 2. Congenital dysplasia: Congenital dysplasia may lead to atrophy and shortening of the penis, which makes the blood vessels stand out as large. 3. Localized varicose veins of the penis: excessive masturbation or frequent sexual intercourse may lead to localized varicose veins of the penis, which will show the coarseness of the penile blood vessels. There may be other reasons for thick blood vessels in the penis, if there is a phenomenon of thick blood vessels in the penis caused by physiological factors, you should go to the hospital in time for diagnosis and treatment.