Based on the mechanism of spiral V notch loosen blasting,uncoupled explosive loading is adopted to prevent the explosion waves from breaking the wall of the blasting hole. Relative parameters of spiral V notch are analyzed and their calculating formulae are achieved. The expressions of the width of the blasted crack,the length of the developed crack and of the sizes of the blasted lumps are obtained. The relationship between the blastyed effect, the spiral angle, and the notching angle is studied, which provides a theoretical base for developing a blasting strategy with desirable lump sizes.