Abstract: Based on the mechanism analysis of blasting extrusion with linear charges,elasto-plastic model of soil and rock under blasting is established in this paper. In terms of state equation of blasting and conservation law of mass,the elasto-plastic calculation formula is provided to calculate extrusion coefficient. 3 types of soil and 2 kinds of explosive are taken as examples to analysis. It is illustrated that blasting extrusion coefficient of soil and rock is related to the density and strength of material. The density and detonation speed of explosive are two additional factors affecting blasting extrusion coefficient.