If one side of the testicle is big and the other side is small, it is recommended to go to the hospital for examination to clarify the specific cause.1. When orchitis or epididymitis occurs, it can lead to an increase in the size of the testicle on the diseased side and a small size of the testicle on the normal side. In acute stage, it may be accompanied by acute pain, swelling or redness of the scrotal skin.2. In testicular syringomyelia, the testicle on the affected side may be slightly enlarged and the scrotum may be enlarged, which is not accompanied by obvious pain, and the scrotum is soft to touch. However, when the amount of syringomyelia is large, the location of the testicle may be difficult to touch, and ultrasound examination of the scrotum is needed to further clarify the situation.3. Varicocele, the scrotum or testicle on the side where varicocele occurs may decrease in size, resulting in atrophy of the testicle. At the same time in the scrotum can feel tortuous, dilated spermatic cord vascular tissue, need to carry out spermatic cord ultrasound to confirm the diagnosis. 4, testicular tumors, when suffering from testicular tumors can appear on the diseased side of the testicular volume increases, accompanied by density hardening, while the normal side of the testicular soft texture, need to carry out testicular CT, MRI and other tests to further confirm the diagnosis.