Based on the mechanism analysis of space form caused by blasting with linear charges, elastic-plastic model of space form caused by blasting was established in this paper. In terms of state equation of blasting and the balance of quality, evaluation formula based on elastic-plastic to estimate space diameter caused by blasting with linear charges was given. The procedure structure of evaluation was introduced. We did 18 experiments on situ and compared experiments results with evaluation ones. They are correspondent very well. Then a new method of evaluating underground space diameters caused by blasting with linear charges was given. The method has more great guidance significance to the optimism plan of the new blasting technology that utilizes the explosion effect of the explosive to compact the soil to form the underground space.