Male erection after the flow of liquid, if there is no discomfort symptoms, may be the prostate fluid, is a normal physiological phenomenon; if the outflow of liquid color, trait abnormalities, may be purulent secretion, may be associated with genitourinary system inflammation. Boys penis erection, if the outflow of liquid colorless and tasteless, or milky white translucent, the patient does not have other uncomfortable symptoms, generally for the prostate fluid. It is part of the semen, earlier than the semen out of the body, can play a lubricating effect. If the outflow of liquid is milky white or yellowish green, purulent with odor, considered purulent discharge, if the patient is accompanied by frequent urination, urinary urgency, urinary pain and other symptoms, may be caused by prostatitis, seminal vesiculitis, urethritis and other inflammation of the genitourinary system. Boys who have purulent discharge, should promptly go to the regular hospital, under the guidance of the doctor, to identify the cause, for treatment, so as not to affect the health of the body.