Mudstone developed in Shihezi group of Daniudi gas field and the inhibitive properties of the drilling fluids are poor, construction safety and progress are seriously affected by borehole instability. Based on the analysis on the instability mechanism, a study on the inhibition of potassium amino polymer drilling fluid was made. Mineral contents of montmorillonite and illite mixed layers were increased to evaluate and optimize higher inhibitive potassium amino based polymer drilling fluid system, which has lower liner expansion ratio and higher roll recovery and is of great practical significance to prevent borehole instability of mudstone section in Daniudi gas field.