To study the shear performance of RC beams strengthened with prestressed CFRP sheets under load, three groups of reinforced concrete beams, total of 12, have been made according to the ratio of reinforcements. In each group, one beam has been chosen to take as contrast beam for single point loading to get experimental data on bearing capacity, as well as fracture distribution. Before the tests, as much as 0.4 times of ultimate shear bearing capacity to the other 9 beams was applied, then the test beams were strengthened at the shear section with prestressed CFRP sheet under load before. Based on the test data, the shear failure mechanism and effect factors of the beams were analyzed. The test result shows that the prestressed CFRP sheets at inclined section could restrain the generation and development of cracks, increase the height of the compression concrete in compression-shear area, as well as improve the shear bearing capacity of inclinded section.