During reconnaissance drilling for polymetallic deposit survey at Qinling Orogenic Belt, different complex strata were encountered, such as collapse, shrinkage, leakage and so on, which seriously affected drilling efficiency. The calcium treated vegetable gum drilling fluid and solid-free polyvinyl alcohol fluid were used for borehole protection, respectively. According to different leakage situations, technical measures such as plugging while drilling, gel plugging were implemented, and good results were achieved.