Kidney stones are located right at the highest end of the urinary system, which consists of four parts: the kidney, ureter, bladder and urethra. If the kidney stone is small in diameter, it may be discharged by itself. The path of discharge is from the renal pelvis to the ureter, which has three narrowing locations: the first narrowing is at the junction of the renal pelvis and ureter, the second narrowing is at the bifurcation of the ureter across the iliac vessels, and the third narrowing is at the junction of the ureter and the bladder. Therefore, the stone will have severe renal colic during the process of discharging the ureter, and after discharging the ureter, it will enter the bladder, and the last stretch is in the urethra, so the stone is finally discharged from the urethra.