Objective: To explore effect of percutaneous nephrostomy under ultrasound guidance for hydronephrosis and evaluation of the clinical value of renal function. Methods: Twenty six cases (thirty kidney) of hydronephrosis underwent percutaneous nephrostomy(PCN). Ultrasonic measurement of renal vascular resistance index(RI) of the interlobar artery and renal parenchymal thickness were performed before and after PCN treatment, and Urine output were recorded everyday. Results: Patients were divided into the functional improved group (22 cases) and the nonfunctional group (8 cases) accordinig to the daily urine output. The preoperative renal parenchyma thickness of the functional improved group was 1.9±0.4 cm, nonfunctional group was 1.1±0.2 cm, there is statistically difference between the above groups(P < 0.01). The preoperative interlobar artery RI of the functional improved group was 0.67±0.07, nonfunctional group was 0.8±0.02, there is statistically difference between the above groups(P < 0.01). The interlobar artery RI of the two groups were significantly reduced after PCN(P<0.01). The thickness of the renal parenchyma were also significantly thickening after PCN (P < 0.01).Conclusion: PCN can accurately assess and effectively improve the renal function, provide certain reference basis for further treatment options.