The crack width directly affects the durability and normal use of structures. In order to investigate the crack resistance of prestressed steel-reinforced ultra-high strength concrete beams, the flexural behaviors of thirteen specimens were tested. Then, this paper analyzes the failure mode and the development and distribution of cracks as well as the maximum crack width were analyzed, and puts forward the relationship between the integrated reinforcement index considering the reinforcement position and the moment under the serviceability limit state was investigated. Based on the existing relevant norms in China, the calculation formula of the average crack spacing and the maximum crack width are proposed, which are appropriate for prestressed steel reinforced ultra-high strength concrete beams. It is found that the calculation results accord well with the test results. In addition, when the web effect is taken into account, the webs of the tension side in a 1/2 beam height range are considered to be equivalent to the longitudinal reinforcement, which leads to the finding that  the calculation values with an integrated reinforcement index of more than 0.19 are slightly greater than the measured ones while the calculation values with an integrated reinforcement index of less than 0.19 are slightly smaller than the measured ones.