The normal sexual function of men includes the processes of sexual excitement, penile erection, intercourse, ejaculation and orgasm. In order to have sexual intercourse, the penis must first be erected; therefore, penile erection is one of the most important and fundamental aspects of male sexual function. Penile erection is a complex psycho-physiological process, which is essentially a series of neurovascular activities. When the parasympathetic nerves are excited, the smooth muscle cells of the small arteries and vascular sinuses in the penile corpus cavernosum dilate, the vascular sinuses of the corpus cavernosum expand, arterial blood flow increases, and the corpus cavernosum of the penis fills with blood and swells. The swollen penile corpus cavernosum compresses the small veins under the white membrane and closes the venous outflow channel. The contraction of the pelvic floor muscles can also compress the corpus cavernosum, making it further swollen and hard and producing erection; when the sympathetic nerves are excited, the smooth muscle cells of the small arteries and vascular sinuses contract, the pressure of the corpus cavernosum decreases, the veins open, and the penis begins to weaken. Therefore, vascular smooth muscle diastole, arterial blood flow blood flow rate and venous blood outflow resistance are the three elements of penile erection. The blood vessels of the penis itself and the supply of blood flow play an extremely important role in the erection of the penis. To use an analogy, the erection of the penis is the same as the storage of water in our reservoirs, the reservoir is full only when more water is fed into it and the gates are closed. The penis is also the same, the arterial vascular expansion after the compression of the veins, reducing the return of penile venous flow, just like the reservoir to close the gate, the more blood filled the more firm. If the arterial blood supply to the penis is insufficient and the arterial blood vessels are not sufficiently expanded, it is like the reservoir is not enough water; or the penile venous reflux is too much, it is like the gate is not closed tightly and the water that went in flows away; if one of these two conditions or both exist, the reservoir will not be full, and by the same token, the penis erection will not be ideal, and if it is serious, it will not be erect.