Double J tube will be placed after some kidney surgeries, and hematuria after surgery is usually normal. Double J tube, also called ureteral stent, is a kind of catheter commonly used after hydrocele, kidney stone or ureteral stone surgery, its function is to support and drain, it is a kind of hollow hose with bends on both ends, the upper end leads into the renal pelvis, the lower end is located in the bladder, to direct urine from the renal pelvis to the bladder, in order to avoid the contamination of ureteral wound. After placing the double J tube after surgery, due to the body’s activities, the double J tube will produce friction with the ureter, especially when walking a lot, the friction caused by the ureter breaks bleeding, resulting in the formation of hematuria, which is an unavoidable and normal phenomenon, it is recommended that postoperative patients who placed the double J tube to reduce the activities, especially to avoid strenuous exercise, and to drink plenty of water, in order to promote urination. If the color of hematuria is darker or the amount of hematuria is more, you should go to the hospital for examination to avoid other situations.