Abstract: An experiment on shear of reinforced concrete beams with high strength rebars was carried out. According to observing the deflection，diagonal crack width and strain of stirrups，the diagonal cracking rules were analyzed. The effects of concrete strength，shear span ratio，ratio of stirrup，section size and section shape on diagonal cracking loads were studied and the calculation method of the diagonal cracking loads was discussed. The results showed that concrete strength，shear span ratio and section size were the major factors for the diagonal cracking loads of reinforced concrete beams with high strength rebars. Meanwhile，the calculation formula of the diagonal cracking loads was suggested，which provided a basis for calculation of the diagonal cracking loads and promoting the use of HRBF500 high strength rebars in practical engineering.