An ionic liquid polymer was synthesized using acrylamide (AM) and bromide N-allylpyridine ([APy]Br) as clay inhibitor. The optimum synthetic conditions were investigated by single factor method. The results were as follows: m(AM):m([APy]Br)=15:1, w(initiator)=0.8%, the molar ratio of K2S2O8 and NaHSO3 was 1:1, the reaction temperature was 50 oC. The polymer was characterized by FT-IR and 1H NMR. It was found that the anti-swelling rate was 80.90% under 2000 mg/L of AM/[APy]Br solution at room temperature, and the anti-swelling rate could remain 77.97% at 90 oC. When 2000 mg/L polymer solution was combined with 0.3 mol/L KCl, the anti-swelling rate could reach 96.09%. 0.2 mol/L KCl combined with 2000 mg/L AM/[APy]Br gave higher anti-swelling rate than 0.3 mol/L KCl solution, and when it was scoured four times, the anti-swelling rate was still 76.17%. The d-spacing of sodium montmorillonite (Na-MMT) was 1.57 nm when soaked in the mixed solution which contained 3.0% AM/[APy]Br and 3.0% KCl, which was less than the d-spacing of Na-MMT soaked in KCl solution(1.62 nm).