〗The drilling formation of WFSD-3 hole is extremely complex with hard, brittle and broken formation and high water sensitivity formation appearing alternately, which brought huge hidden danger to the drilling construction. According to the special formation situation of the hole, based on the borehole stability theory analysis and the laboratory experiments, NH4-HPAN, K-PAM, SAS and KHm inhibitors had been selected out as the optimized additives for the mud system. In addition, the laboratory sand-bed non-filtration experiments and the ZNP-01 shale swelling experiments had been carried out to evaluate the blocking and inhibitory capacity of the mud formulations. This mud system has satisfactory application effects. The paper also summarized some treatment technologies in the application of mud maintenance, such as mud viscosity and gels control technique, the drill bit anti-balling technique and calcium invasion treatment technique while drilling cement plug, which have a good reference to drilling in the complex formation.