Inclusion Criteria:  Patients consent for percutaneous renal stone removal. Kidney stones 2-4cm. Aged 18-70 years. Normal renal function. ASA scoreⅠ-Ⅱ.  Exclusion Criteria:  Severe cardiopulmonary dysfunction or cardiopathy. Coagulation dysfunction. Pyonephrosis or severe acute infection. Transplanted kidney, solitary kidney, horseshoe kidney, urinary diversion, urethra deformity. Other procedure was required in the same session of operation.