ＪＲＣ是反映爬坡角力学效应的岩体结构面表面形态等效描述指标。本文在爬坡角力学效应机理研究基础上，阐述了ＪＲＣ直边法的物理意义；通过岩体结构面表面起伏幅度与金属表面粗糙度幅度对比分析，肯定了直边法的合理性；考虑ＪＲＣ的尺寸效应，推导ＪＲＣ修正直边法的数学表达式，编译计算机常用程序。最后，实例检验了ＪＲＣ修正直边法数学表达式的合理性和可用性。 JRC is an equivalent description of the surface morphology of rock mass structure that reflects the mechanical effect of climbing angle. In this paper, based on the mechanism research of mechanical effect of climbing angle, the physical meaning of JRC straight edge method is expounded. Through comparison and analysis of the amplitude of surface fluctuation of rock body structure surface and the roughness of metal surface roughness, the rationality of straight edge method is affirmed; The size effect, deducing the mathematical expression of the JRC correction straight-edge method, compiling the computer common program. Finally, the example tests the rationality and usability of the mathematical expression of the JRC modified straight edge method.