On the basis of two dimensional seepage flow calculation of the earth-rock dam at the left bank of the Danjiangkou Dam, some questions about the notch of cut off wall, which length is 40 meters, at the connecting section of the earth-rock dam and the concrete dam was mainly taken into accounted. According to the combination of disadvantage parameters, the seepage state and the effect of static pressure grouting of the core wall with or without vertical cracks was analyzed using three dimensional finite element program of seepage calculation. The calculation showed that the injecting cement paste can make up the partial size shortage of the core wall of the old dam effectively. When the core wall occurs in some extreme conditions such as both transverse and vertical cracks simultaneously, it can control the leakage effectively. The seepage stability of the contact region of the bottom of the core wall and the bedrock, as well as the region of the core wall and the concrete dam, were also evaluated.