Through the experiment of the four RC beams strengthened with SWR externally prestressing, the shear resistant effect of Strengthened beams under cracking width of the original beams is studied in the paper. The ultimate load was confirmed by the test of the basic beam. First the presplitting load were respectively 50%, 60%, 70%, 80% of the ultimate load of basic beam, and seconly cracks were repaired with JN-L low viscosity pouring sealant, lastly experiment beams were strengthened by shear reinforcement of the external prestressing with steel wire rope. Loading method is the single point loading, and the shear span ratio is 2.0. The results show that: the cracking width of original beam has certain effect in shear resistant capacity. When the cracking width was less than 0.2 mm, the effect of injecting glue was not ideal and the shear resistant capacity is lower. When the crack width was bigger, the effect of injecting glue was more ideal, so the effect of reinforcement was better. When the cracking width was greater than 0.28 mm, the ultimate load was no longer improved. The smaller inclined cracking width in strengthening is, the worse repairing effect and the bigger strain value of stirrup is. Each strengthened beams’ wire rope strain increment was nearly close before cracking. As the decrease of original beams crack width, crack repair effect was weak, and the external strain increment of wire rope becomes bigger under the same load. The trend was very clear after the stirrup yielding.