Percutaneous nephrolithotomy (PNL) has been considered as the first-line choice for the management of >20mm kidney stones. Microchannel percutaneous nephrolithotomy (Mini PCNL) which takes nephrolithotomy channel size less than or equal to 18, was first used in the treatment of children with kidney stones in 1997, then gradually applied to adult, aims to achieve the similar stone clearance rate as the standard channels, at the same time, reduce the complications. At present, the use of percutaneous renal surgery in our country is more than 18F plastic peel-away sheath, with the access sheath with a suction-evacuation function was first used by Guohua Zeng and so on. But there is still a lack of high quality evidence of Evidence-based medical evidence to compare the two kinds of sheath for the safety and effectiveness. Therefore, this study provides a reliable theoretical basis for the choice of the sheath for the treatment of 2-5cm size Kidney, and ultimately benefit patients with 20mm.