This paper is based on the experiment results observed from 15 different section size beams subjected to the monotonic loading and the low reversed cyclic loading. In order to study the effect both on the section size and the variation laws for the plastic hinge length, four approaches were used to explore the variation laws when the load surpassed the yield point of the reinforcement to the limit displacement point. The analysis results show that after the yield load, the more the increase of the load, the more the increase of the plastic hinge length. It means that the plastic hinge length shows the size effect obviously. When section heights increase from 200 mm to 1 000 mm, the relative plastic hinge length of the specimens subjected to the monotonic loading shows that the peak load point and the limit displacement point are reduced by 40% and by 44%, respectively, and by 38% and by 40% for the low reversed cyclic loading. The results calculated from the proposed approaches which are considered to be the influential factor of the sectional height, agree well with the experimental results.%为了研究钢筋混凝土梁塑性铰长度随荷载的变化规律及其尺寸效应，依据15根不同截面尺寸的钢筋混凝土梁单调和低周往复加载试验结果，分别采用4种方法探索了塑性铰长度从屈服点到极限位移点的变化规律，研究了截面尺寸对梁试件塑性铰长度的影响。结果表明：屈服荷载后，随荷载的增加塑性铰长度逐渐增加；塑性铰长度表现出明显的尺寸效应。截面高度由200 mm增加到1000 mm时，单调试件的峰值荷载点和极限位移点的相对塑性铰长度分别降低了40%和44%，低周往复加载试件则分别降低了38%和40%。在此基础上，提出的考虑截面高度影响系数的塑性铰长度计算值与试验值吻合较好。
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