Through the development of X-diffraction, coefficient of rolling recovery and expansion laboratory experiments, the physical and chemical performance distribution rule of the formation clay mineral in Baka area was summarized. According to characteristics of formation lithological and technical difficulties of the drilling fluid used in Baka area, combined with the existing several different drilling fluid systems, including sulphonated polymer mud, polyether glycol drilling fluid, and amino poly alcohol drilling fluid, the conventional performance, inhibition performance and plugging and anti -sloughing ability were investigated and the best drilling fluid was carried out in t Ke21-ping 1 well. The experimental results showed that the content of coal and clay minerals were higher, thereinto, the clay minerals were mainly illite and smectite mixed layer, which meant that the drilling fluid in coal seam drilling hole should have strong inhibitory, in the lower should have anti-sloughing ability. The recipe of the optimal drilling fluid system with the strongest inhibitory and plugging and anti-sloughing ability, an amino poly alcohol drilling fluid, was as follows: (4%-5%) bentonite+0.5% amino poly alcohol AP-1+0.5% aluminum polymer anti-sloughing agent DLP-1+ (0.8%-1%) Hydrolyzed polyacrylonitrile sodium NaHPAN+0.5% NaOH+ (0.3%-0.5%) carboxymethyl cellulose CMC+ (3%-4%) cationic emulsified asphalt +3% sulfomethylation phenolic resin SMP-1+ (3%-5%) sulfomethylation phenolic resin SMP-2+3% lignite resin SPNH +2% non-invaded protection agents BST-2+3% sulfonated tannins SMT+ (2%-4%) sulfonated humic acid chromium PSC. The API filtration of the optimal drilling fluid was 4.2 mL, and the high temperature and high pressure filtration was 12 mL, which could inhibit shale hydration swelling effectively, exhibiting the excellent plugging and anti - sloughing ability. Field test results of Ke21 - ping 1 well showed that in the coal seam section drilling process the underground complicated accidents had not occurred to, and the penetration of many sets of coal seam and coal-bearing stratum was achieved successfully. At the same time, it also ensured the stability of directional drilling of borehole wall, and made the drilling cycle significantly shorten and the performance of drilling fluid maintenance more easily. The operation was simple and could fulfill the safety drilling requirements of coal seam hole.