1, abnormal or lack of internal spermatic vein valves. The lack of valve in the left internal spermatic vein near the renal vein is about 40%, and the valve insufficiency is about 10%. 2.The left internal spermatic vein is longer. 3, The left internal spermatic vein confluences with the renal vein at right angles. 4.The renal vein pressure is higher than the inferior vena cava pressure. 5.Compressed by the content of the descending colon or by the angle between the superior mesenteric artery and the aorta. 6.The pressure of the thoracic and abdominal cavities and the effect of venous pressure caused by the upright state in humans.