In order to objectively and exactly express the damage caused by blasting in fractured rock, on the basis of the fruits of predecessor's research, this paper introduces damage variable to express primary damage degree of fractured rock, adopts the damage criterion of rock to educe the formulas for calculating the radii of crushed and fractured zones in fractured rock at annular uncoupled charge blasting. The formulas show that the scope of damage zones are affected by not only radius of blasting hole and characters of power and rock but also primary damaging degree of rock and uncouple coefficient used. Taking Wulongquan Mine as an example, this paper adopts educed formula to calculate the radius of fractured zone , which is expressed by uncoupling coefficient.