Aluminium oxide fiber (AOF) is a new type of polycrystalline ceramic fiber material with good hydrophilicity. Aluminium oxide fiber modified concrete (AOFMC) was prepared by using AOF as modified material. By testing AOFMC compressive strength, flexural strength and splitting tensile strength, the effects of AOF content and length on the mechanical properties of concrete were analyzed, and the optimum content and length of AOF were determined. On this basis, the strengthening effect of AOF on the mechanical properties of concrete with different strength grades(C40, C50, C60) was studied. In addition, the effects of AOF on the microstructure of concrete were analyzed by scanning electron microscopy and mercury intrusion test. The results show that the effect of AOF content and length on the improvement of mechanical properties of concrete is mutually restricted. When the length of AOF is 12 mm and the volume content is 0. 2% , the mechanical properties of AOFMC are the best. With the increase of strength grade, the improvement effect of AOF on the mechanical properties of concrete is increasing. AOF is well combined with concrete matrix, thus improving the mechanical properties of concrete. In C50 concrete, AOF is mainly pulled out, while in C60 concrete, AOF is partially pulled off. When the length of AOF is small, AOF can fill the internal pores of concrete.