Abstract: Regarding the crack development of concrete beams reinforced with fiber-reinforced polymer (FRP) bars as a process wherein the FRP bars are pulled out from concrete on both sides, a differential equation of crack width of lightweight aggregate concrete beams reinforced with FRP bars considering bond-slip behavior was established. According to the crack width limits provided by the design codes, the upper limit of slip was reasonably determined and constitutive models for bond-slip relationship between FRP bars and steel fiber reinforced-lightweight aggregate concrete in ‘low slip’ stage which were suitable to the service stage of the beams were proposed and introduced. The maximum crack spacing, l_max, amplification factor of crack width, h₂/h₁, and residual stress of fiber reinforced-concrete in cracked sections, σ_fib, were specified. On this basis, a crack width model of steel fiber reinforced-lightweight aggregate concrete beams reinforced with FRP bars was proposed using iterative algorithm and its accuracy was evaluated based on measured data of maximum crack width in service stage. It is shown that within crack width limit of 0.5 mm, the proposed model generates accurate maximum crack width predictions for steel fiber-reinforced lightweight aggregate concrete beams reinforced with FRP bars.