There are many factors that can cause pain in a line under the testicle, such as epididymitis, varicocele, chronic prostatitis, urinary tract infection and so on. 1. Epididymitis: bad sex or urethra infection will cause inflammation along with the vas deferens to retrograde the epididymis and cause inflammation, which will lead to pain in the line under the testicle. 2. Varicose veins of the spermatic cord: the reduction of elastic fibers in the vein wall or the increase of venous pressure and other factors will lead to varicose veins in the spermatic cord, and circulatory disorders will cause pain at the bottom of the testicles. 3. Chronic prostatitis: when the prostate gland is infected by microorganisms such as fungi and mycoplasma, it will cause an inflammatory reaction in the prostate tissue, which will lead to pain in the bottom of the testicle with a line. 4. Urinary tract infection: when pathogenic bacteria attack the urinary system of the human body, it may lead to infection of the urinary tract and cause pain at the bottom line of the testicles. In order to find out the cause of pain in the line at the bottom of testicle as early as possible, it is recommended to go to the hospital in time.