Abstract: The amphoteric polymer FA-367 and XY-27 are additives with highly inhibitive character. Applications in Henan Oil Field and Talimu Oil Field testified that the combination of FA-367 and XY-27 had highly inhibitive effect, and hydrated swelling and dispersion of mud shales could be inhibited effectively. FA -367,with strong encapsulation and flocculability, is a good fluid loss agent, and XY -27 has a wonderful shear - thinning effect:The drilling fluid system has the advantages of reducing additives, simplifying maintenance, good lubricity, no toxicity and no contamination. By utilzing the system, rate of penetration can be improved, wellbore enlargement is able to be reduced, and downhole problems can also be decreased. Besides, mud discharge scale can largely be reduced, it is advantageous to the environmental protection.