Objective Discusses the application of different dose of CT scan in the clinical diagnostic value of urinary calculi. Methods In chronological order according to admission registered 200 cases of suspected urinary calculi were divided into a control group and the observation group, the 100 cases respectively. Control group with conventionaldose CT scan (120KV, 150mA); Observe the different groups were used (100mA, 80mA, 50mA) low-dose CT scans based on patient body mass index. Comparison of the two groups were image quality score (IQS) and volume CT dose index (CTDIvol), scanning sensitivity, specificity, positive predictive value, negative predictive value. Results The study found that the observation group CTDIvol was (6.5±1.1) and the control group (19.7±1.4) compared with statistical significance (P <0.05); but the two groups scanning sensitivity, specificity, positive predictive value, negative predictive value , IQS comparison, no significant difference (P>0.05). Conclusion Compared with conventional dose CT scan, according to body mass index (bmi) in patients with clinical use of lowdose CT scan, the images quality, specificity, positive predictive value and its quite. But low dose CT scanning process produced less radiation dose, therefore cause harm to patients, more worthy of popularization and application.