Abstract: During horizontal well drilling in high permeability carbonate reservoir of the YD Oilfield, many challenges were encountered, such as borehole instability, salt and gypsum contamination, lost circulation, poor hole cleaning, and high friction drag. In order to solve these problems, laboratory experiments have been done to optimize fluidity regulator, anti-salt filtrate reducer, complex lubricant formula and plugging materials, and then emulsion polymer drilling fluid with strong inhibition and good plugging property was developed. Moreover, drilling fluid maintenance technique for every formation with different geologic feature has been conducted. With the application of the developed drilling fluid, shale rolling recovery rate could get 88.2%, its linear expansion rate could get 18.2%, and 5.0% NaCl or 2.0% CaSO4 or 30% drilling cuttings contamination could be resisted,which showed that the developed drilling fluid has strong anti-sloughing function and good resistance to contamination.The drilling fluids have been applied in three horizontal wells in the YD Oilfield, including Well S4, Well S5 and Well S16, and kept stable performance in drilling operation.Compared with 22 offset wells, the drilling duration of these three wells has been reduced by 5.2 d, 6.3 d and 7.8 d respectively, the leakage volume has been reduced by 12.5%, 8.4% and 13.2% respectively, and the resistance while RIH and POOH can be less than 150kN. The application results show that the developed drilling fluid can solve horizontal drilling problem in carbonate formations with high permeability, and can be used widely in the YD Oilfield in the future.