Abstract: The flexural testing of concrete beams with 600 MPa high strength steel bars was carried out. Studied was the effect of concrete strength, of strength and ratio of reinforcement on the deflection of beams tested. In the serviceability limit state, the utilization ratio of bearing capacity (M/M_u) of test beams decreased with the increase of reinforcement ratio, and the positive effect of concrete strength decreased with the increase of reinforcement ratio on the deformation resistance of test beams, and the deflection of test beams with high strength steel bars was larger than that of ordinary steel bars (HRB400) after equal strength substitution with ordinary steel bars, and after equal volume substitution, the ultimate bending moment was increased by 28.6% and when the same M/Mu value is reached, high-strength reinforced concrete members produce larger deflection. The test value of deflection was larger than the calculated value by the current code for test beams, which also verified the applicability of the formula derived by other scholars. Finally, the formulas were modified for the current code according to the test data. The first method was to introduce an equivalent stiffness reduction coefficient based on the short-term stiffness formula of the current code. The other method is to conduct a regression analysis for the test data, and the new short-term stiffness formula was presented. The results show that the two methods proposed illustrate their good accuracy.