Ureteroscopic lithotripsy (RIRS) is the first-line treatment for 1-2 cm upper urinary tract stones, and the stone clearance rate can reach 81.4% - 92.5%. Fever after RIRS is the most common infection after RIRS, and its incidence is up to 20%. The incidence rate of systemic inflammatory response syndrome is 6.5% - 10.3%, sepsis 0.1% - 4.3%, with the infection progressed. If there is no timely and effective intervention in the early stage of urogenic sepsis, it can progress to septic shock, and the mortality can be as high as 30% - 40%. High intrarenal pressure is an important risk factor for postoperative infection. American Urological Association (AUA) guidelines point out that controlling intrarenal pressure at an appropriate level is particularly important to prevent postoperative infection.

The use of ureteroscopic sheath in ureteroscopic surgery can effectively reduce the intrarenal pressure, which is an important measure to reduce the incidence of postoperative infection. Theoretically, the larger the space, the better the reflux effect and the lower the incidence of postoperative infection. The study showed that the incidence of ureteral sheath infection was significantly lower than that of ureteral sheath infection after operation. When using the same caliber ureteroscopic sheath, use a smaller caliber ureteroscopy to increase the space between the ureteroscopy and the ureteral sheath, promote reflux, reduce intrarenal pressure and reduce the incidence of postoperative infection. However, there is still a lack of relevant research on the effect of different caliber ureteroscopy in the treatment of renal calculi on postoperative infection.

Inclusion Criteria:

1. Agree to receive ureteroscopy
2. Aged 18-70 years. 3.1-2cm kidney stones

Exclusion Criteria:

1. Combined with middle and lower ureteral calculi, surgical operation other than RIRS is required;
2. Patients with abnormal anatomical structure, ureteral stenosis and urinary diversion, such as ectopic kidney, horseshoe kidney and duplicate kidney;
3. Patients who have undergone nephrostomy;
4. Severe cardiopulmonary insufficiency;
5. Pregnant women.