Air DTH hammer drilling is a preferred technology in bed rock area， which by tradition is suitable for hard rock drilling(in hard, brittle and broken formations); while for loose formations, conventional mud rotary drilling or percussive drilling should be used. Based on the test on typical unconsolidated formation drilling, it is proved that normal drilling can also be realized in loose overburden layer by air DTH hammer with advantages of high efficiency, low cost and small labor intensity, the highest drilling efficiency is up to 87m/h and 72m/h in clay and moist clay drilling respectively. This result provides an effective method to hole opening or the first spud section drilling for the exploration of shale gas, geothermal energy, coal seam gas and underground water in overlaying layers and solves the water shortage for drilling fluid in water scarce areas or serious leakage formations and avoids the difficulties in the complicated processes of conventional mud rotary drilling.