Recent advances in the research on erectile dysfunction (ED) has more clearly explained the mechanism of penile erection, which is a hemodynamic process involving relaxation of corpus cavernosum smooth muscle and related arterials, and NO-cGMP signaling pathway proven to play an important role on modulating the relaxation of corpus cavernosum smooth muscle. Studies on NOS and PDEs not only provide strong evidence for the clinical treatment of ED, but also provide the chance to develop Sildenafil. Although the gene therapy for ED is still in the laboratory stage by now, it may be one of the effective clinical therapies for ED in future.