Abstract: Objective: This study aimed to investigate the application value of fractional bolus injection of a contrast agent combined with double-layer detector spectral CT 50 keV virtual monoenergetic imaging (VMI) in combined imaging of computed tomography urography (CTU) and aortic CT angiography (CTA). Methods: The experimental group included 32 patients who underwent spectral CTU with a Philips IQon dual-layer detector at Beijing Tongren Hospital, Capital Medical University, between March and April 2024. Using fractional bolus injection of a contrast agent and bolus tracking technology, the conventional 120 kVp mixed energy image was reconstructed after scanning for group A1; the 50 keV VMI obtained by spectral reconstruction was group A2. The control group included 32 patients who underwent CTU examination between December 2023 and March 2024 using the same equipment, and the contrast agent split bolus and group injection tracking techniques were used. After scanning, the conventional 120 kVp mixed energy image was reconstructed for group B. The objective evaluation included the CT value, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) of the abdominal aorta and bilateral renal arteries, which were compared among the three groups. The Kruskal–Wallis and Nemenyi tests were used to compare the average CT values of the initial, middle, and lower parts of the ureter. Wilcoxon test was used to compare the effective radiation dose between the experimental and control groups. Subjective evaluation was performed by two senior radiologists on the three groups of CTU and CTA images using the 4- and 3-point methods, respectively. The consistency of the subjective scores of the two radiologists was analyzed using the Kappa test. Results: Among the objective evaluation indices, there were statistically significant differences among groups A2, A1, and B. There was a significant difference in the SNR of the bilateral renal arteries between groups A1 and B. The effective radiation dose of the experimental group was 15.1% lower than that of the control group, which was significantly different. There was no significant difference in the subjective evaluation of the CTA and CTU images among the three groups. The consistency of the CTA and CTU image scoring results between the two physicians was excellent and good, respectively. Conclusion: If CTU examination was performed by fractional injection of a contrast agent, fusion images of the urinary system and aorta were obtained, which not only had a clear anatomical relationship and the same image quality, but also reduced the effective radiation dose. The 50keV virtual monoenergetic image obtained by spectral reconstruction optimizes the image quality of CTU and CTA and has clinical value.