Among the slope slide affairs in rock engineering, most of the slide affairs are influenced by joints and cracks in rock-mass. The joints and cracks deeply concern with sliding plane. The study of joints and cracks becomes main content of rock mechanics. The joints and cracks formed in long geological history, and became somewhat trench, somewhat scale, somewhat shape, which influencing the rock-mass character. Block Theory is one of the useful tools to analyze slope stability of crack rock mass, but it has some shortcomings. In this paper the Authors make modification to block theory and apply the modification in analyzing slope stability.
KEYWORDS: Block theory, Modification, Application, In situ