Abstract: The feasibility of slope reinforced by grouting is proved and multistage grouting(PG) is put forwatd. Based on the traditional theory of fill grouting, penetration grouting, compaction grouting and hydrofracture grouting, the formula of grouting press,grouting radius and grouting stress of multistage grouting in different phase and stratum is deduced by the introduction of the elastic and plastic theory about glob and column expansion,Boussineq's and Terzagh's theory. The calculation model for multistage grouting design and statistical rule of concrte-clay from a lot of experiment and test data is summarized. The multistage grouting model is testified by the engineering practice.