Using shear overstrength factors is one of key earthquake resisting measures for reinforced concrete (RC) frame members,which aims to ensure the safety of structures under rare earthquakes. The shear overstrengh factors for different seismic grades have been provided in Chinese code,while little research has been conducted up to date which focused on the actual effect of shear overstrength factors. Three regular RC frame structures were designed according to the current code,which respectively located in intensity region 7(0.15g),8(0.20g) and 9(0.40g). Nonlinear dynamic analyses under rare earthquakes were finished.The ratio of the shear demand under rare earthquakes to the average shear capacity for beams and columns was calculated to identify the effectiveness of the shear overstrength factor. The rule is that the ratio of more than 90% components are less than 1.0. The adjustments were made in the case when the shear overstrength factor did not meet to the rule,which continued until that the factor is up to grade. The result proves that shear overstrengh factors for RC frame beams can keep on; the shear overstrength factors for first seismic grade is oversized,while that for second and third seismic grades can not satisfy the shear demand. Two sets of schemes for column shear overstrengh factors are proposed based on further analysis.