This paper presents the results of injection analysis to understand the injection process of cement grout into the rock voids. The injection process into the rock voids is classified into three large processes. There are a transportation process of cement particles, a clogging process in the rock voids and a hardening process. In the analysis, the clogging process and the transportation process were analyzed. As to the analysis of the clogging process, the material transport equation considering the filtration theory was introduced and used. As to the analysis of the transportation process, the equation of the plug flow that was related to Bingham fluid instead of Darcy's law was expanded and used. From the results of these analyses, the existence of grout concentration corresponding to the purpose was suggested.