Foundation treatment is usually difficult for large water conservancy project on the mudstone which generally has poor geological conditions. The dam foundation of Hattashan hydro-junction project was constructed on flat mudstone; the stability and security of the dam foundation were seriously affected by the deep layered fracture zone. Analysis on the outgush infiltration channel was made and a series of grouting method were taken. This approach not only saves cost, but also ensures the construction quality. The article summed up the treatment method of special gushing water in the mudstone on the basis of the large water inrush in powerhouse water collecting well and in the P7 fracture zone; it is worth to be the reference.