Stemming length is one of the most important parameters during the raise excavation by one-step deep-hole blasting. For properly determining the blast-hole stemming length and improving the blasting effect of one-step deep-hole blasting, a study is carried out. Rock fragmentations are checked up to analyze how stemming length has an effect on raise excavation by one-step deep-hole blasting. Based on the material characteristics of hole stemming and the theory of elastic-plastic mechanics, the deformation calculation model of stemming under the explosion load has been set up. Based on the energy transfer in the process of deformation and movement, and the relation among the time when the stemming moves out of the hole, the time that rock crushes, the time that blasting crater forms, and the time that adjacent stratified rock starts to break, the stemming theory of one-step deep-hole blasting has been deduced from the theorem of kinetic energy. In the experiment with a 32 meters filling up raise located at Sandaozhuang mining area, the stemming theory is applied to; combining with the actual engineering geological conditions, the actual stemming length is selected, an explosive solution is formed, and the raise excavation by one-step deep-hole blasting wins a success. And the stemming theory has been verified and it provides the guidance for raise excavation by one-step deep-hole blasting.