Abstract: To study the flexural behavior of an ultra-high-performance concrete (UHPC) one-way slab reinforced with fiber-reinforced polymers (FRP) bars, the flexural tests of nine UHPC one-way slabs were conducted. Analyzed was the influence of bar type, of reinforcement ratio, of reinforcement mode and of confinement condition in the compressive zone on the flexural performance of the slabs. The results show that compared to wrapped FRP bar, the utilization of hot rolled steel bar and indented FRP bar with a better bond in UHPC can decrease the average crack spacing by 8.2% and 6.7%, respectively. Placing a layer of basalt fiber-reinforced polymers (BFRP) grid in the compressive zone can increase the ultimate compressive strain of UC150 by 8%, leading to that the flexural capacity and ductility index of the slab increased by 13.3% and 23.1%, respectively. Based on the results in this study and on other references, modified were the uniformity coefficient of FRP strain and the average crack spacing in the standard of GB 50608−2020. The calculation equation for FRP stress was developed, where the tensile resistance of UHPC was considered. For the wrapped FRP bar, smooth gird and indented FRP bar, the bond-dependent coefficient ν_i was suggested as 0.7, 0.8 and 1.0, respectively. The mechanical property coefficient of a structural member in the code of JTG 3362−2018 was used to consider the effect of sectional depth on crack development. Accordingly, proposed was the method for calculating the crack width of a FRP reinforced UHPC one-way slab or a beam.