To make the drilling process more efficient and successful against drilling complex formations while penetrating through deep thick overburden layer at Badi hydropower station over the Dadu river, 139 thick-walled casing and vegetable gum were used to improve coring quality and drilling efficiency respectively. 139 thick-walled casing can avoid frequent drilling accidents and shallow depth in casing process and is compatible with 108 casing much better than 127. It is proved that this technology can give good coring qualityand satisfy drilling efficiency with lower drilling cost and higher economic benefits.