Based on Code for design of concrete structures (GB 50010—2010),six knee joints with HRB500 rebars on top story of reinforced concrete frame structure were designed and tests on their seismic behavior were conducted under reversed cyclic loading. The effectiveness of code provisions on seismic detailing of such knee joints of reinforced concrete frame was revealed. Mechanic properties, failure modes and comprehensive seismic performance of these top story knee joints reinforced with 500 MPa rebars was analyzed. Furthermore, these joints were compared with those similar joints reinforced with 335 MPa rebars. Different ductility index were used to discuss difference of ductility of joints reinforced with different strength rebars to provide reliable evidence for the application of 500 MPa rebars in the joints.