Objective Discussion and analysis of urinary tract obstruction in patients with low radiation and the effect of low dose contrast agent MSCTU. Methods Select our hospital from January 2012 to December 2012, admitted during the period of 120 patients with urinary tract obstruction were studied. According to different grouped into conventional CT tube current dose group (190-260 ma) and 190 ma and 80 ma group. Using spiral CT scanning. 100 ma and 80 ma group: scan before, through the center of the elbow vein in patients with one-time push 20 ml contrast medium injection, discharge phase scanning of the reentry after 15 min. Routine group: patients with high pressure injector in the center of the elbow intravenous 80 ml contrast agent, the injection rate of 3-3.5 ml/s, and in patients with abdominal conventional three phase scanning and discharge phase scanning, and study the discharge images. After the scanning, need for MPR and VR and MIP, CRP, reconstruction. Group and select the conventional image as a standard to evaluate the other two groups of image quality. Results The study found that three groups all period of cross-sectional images and ureter and kidney in urinary system MIP and VR images comparison (P>0.05). And 80 ma group and routine group, 80 ma and 100 ma set of pairwise comparison, the ureter middle period of cross-sectional images and MPR and CRP image comparison (P<0.05). However, bladder crosssectional images: 80 ma and 100 ma group comparison (P>0.05); 80 ma group compared with normal group (P<0.05). Conclusion Clinical diagnosis of urinary tract obstruction, when will the tube current to 80 ma, contrast medium to 20 ml, can be on patients with MSCTU accurately upper segment ureteral obstruction and renal collecting system. But tube current is 100 ma, contrast medium for 20 ml, its image is more clear, can make accurate diagnosis to the urinary tract obstruction.