Abstract: This paper was based on the text results of 12 different section size columns under monotonic loading and low reversed cyclic loading. In order to study the effect of section size on plastic hinge length, four methods were used to determine the plastic hinge length of the specimens: longitudinal rebar yield, “longitudinal rebar strain-section curvature”, “dial gage-section curvature”, equivalent plastic hinge length. The analysis results show that the four methods used to determine the plastic hinge length have certain differences. Result of equivalent plastic hinge length is the minimum; result of method“dial gage-section curvature”is the maximum. Plastic hinge length relatively decreases with increasing of cross section size. Then, on the basis of experiment, the section size effect coefficient of plastic hinge length was proposed.