Abstract: To study the influence of fiber distribution on the mechanical properties of Reactive Power Concrete(RPC) members under quasi-static loading, the four-point bending test was carried out on RPC specimens at the same fiber content (2%) and different fiber lengths (13mm~20mm). By selecting the initial crack point, peak point and other characteristic points on the bending load deflection curves, the bending properties of aligned steel fiber RPC(ASFRPC) and steel fiber RPC(SFRPC) were analyzed quantitatively. The experimental results follow: Orientation coefficient of steel fibers has a strong impact on the deflection hardening behavior in bending. First of all, the bending tensile peak stress of ASFRPC is greater than that of SFRPC. In particular, when the mid-span deflection reaches L/150, the residual strength of ASFRPC specimen is still 4.35 MPa~6.9MPa higher than that of the initial crack strength. Secondly, when the fiber length increases from 13mm to 20mm, the flexural property of ASFRPC specimen improves more significantly than that of SFRPC specimen, and the load of the aligned distributed steel fiber specimen is also greater. Thirdly, the fiber distribution of ASFRPC is uniform at the fracture, most of which are perpendicular to the main crack direction. Besides, the anchorage length is also long, and the bridging effect is significant at the fracture. In conclusion, considering the equivalent bending stress and energy absorption capacity of ASFRPC specimens, the mechanical properties of aligned steel fiber specimens perform best when the fiber content is 2% and the fiber length is 20mm. Keywords: aligned steel fiber; Reactive Powder Concrete; fiber length; the equivalent bending stress; toughness