Abstract:At present,the relation of the macroscopical and microcosmic parameters through the macroscopical parameter or the microcosmic fracture toughness test has seldom been found. The damage will initialize in the rock mass during unload because of the cutting;and it is difficulty to define the relation from the laboratory test and another parameters. However,there is a relation between the macroscopical and microcosmic parameter. A series of equations are proposed for the relation about the geological strength index(GSI) and the fracture toughness K. It is found that the results achieved from the equations agree well with those of in-situ test and laboratory rest.