Four lightweight aggregate concrete beams with plastic steel fiber content of 0kg/m³, 3kg/m³, 6kg/m³, 9kg/m³ were produced, to study the effect of plastic steel fiber on the flexural properties of lightweight aggregate concrete beams. The results show that plastic steel fiber effectively delay the development of beam cracks and reduce the maximum crack width and make the cracks much denser. The cracking moment and the ultimate moment increase with the proportion of plastic steel fiber, the cracking moment and ultimate moment of the LC-9 beam are increased by 72% and 8.43%, respectively, compared with the LC-0 beam. With the fiber content increases, the yield deflection of the beam increases and the ultimate deflection increases. Meanwhile the deflection ductility coefficient μ_f increases, with a maximum increase of 92.23%. The plastic steel fiber reduces the height of the relative compression zone of the beam, the load-holding capacity is improved, and the strain of steel bar is reduced, and the yield time of the steel bar is delayed.