For being situated in a mined out area, the foundation was unstable in CK3 contract section of Yangcheng-Manghe section of Yangcheng-Jiyuan expressway, the full filling pressure grouting method was used in the treatment. Because mud was restricted and hole completion was difficult in gravel layer, high pressure DTH hammer was applied with good effect. This paper summarizes the construction experience of grouting boring in mined-out area with high air-pressure DTH drilling technology in grouting hole design, equipments selection, BHA & drilling technology and dust & pollution control, which can be reference to the mined-out area treatment for the similar project.