One testicle on one side and one testicle on the other side may be caused by physiological factors, overstimulation, testicular torsion and other factors. 1. Physiological factors: under normal circumstances, the testicles on both sides of the male are not exactly the same, there may be a slight difference, manifested as a high one and a low one or different sizes, as long as there are no other abnormalities, there is no need to worry too much. 2. Excessive stimulation: for example, foreign object stimulation or hand stimulation of testicular area may cause unilateral contraction of testicular muscle, testicular uplift, which will lead to one testicle up and one testicle down, reasonable rest and removal of stimulating factors, can be restored to normal. 3. Testicular torsion: it may be related to poor posture or testicular trauma, which may lead to testicular torsion, which will make the testicles go up and down one by one, accompanied by severe pain, swelling and other symptoms, and in severe cases, it may lead to ischemic necrosis of the testicles on the affected side. If the testicles are in an upward and downward position and accompanied by other obvious abnormal symptoms, it is recommended to consult a doctor in time for examination and treatment.