Abstract: With the city developing faster, land is becoming more precious, high——rise buildings are growing rapidly, to meet the growing needs of the structural loads, pile length and pile diameter gets more greate. Without increase in costs, post grouting technique improves bearing capacity of cast——in——place pile, and lowered the settlement of building, it has been more used. This paper introduces the improvement mechanism of post grouting pile and several engineering examples, analysis the change of bearing capacity of single pile grouting before and after grouting, and application accumulated some material.