The invention discloses a fast high efficiency preparation acrylonitrile polymer method. It includes the following steps that the first monomer acrylonitrile, the second monomer acrylic acid methyl ester, the third monomer itaconic acid, and initiator are added into ion liquid orderly. It is churned and done polyreaction for 0.5-4h at 50-80 centigrade degree. Then acrylonitrile copolymer is gained. The benefit effects of the invention are that the polyreaction rate is increased greatly; the conversion is increased greatly; the adopted ion liquid has no volatility; and this is of great advantage to reclaim the ion liquid; the liquid state range of the adopted ion liquid is wide; and this is of great advantage to control reaction temperature.