The Kunbei glutenite reservoir has thick layer and strong heterogeneity in plane, interlayer and intralayer. In the early stage of development, the horizontal well production yield decreases and water cut rises rapidly. Horizontal wells are in urgent need of water control. Based on the characteristics of Kunbei reservoir and production, Acrylamide (AM)-2-acrylamido-2-methylpropanesulfonic acid (AMPS)-dimethyldiallylammonium chloride (DMDAAC) terpolymer selective water shutoff agent for horizontal wells was synthesized. The injection performance of water shutoff agent was investigated by rheological mechanics experiment, and the selectivity of water shutoff agent was investigated by core plugging simulation experiment. The core experiment shows that the injection pressure is increased by 6.06 times after water plugging, the water flooding plugging rate is 83.5%, and the oil displacement plugging rate is 20%, which has remarkable oil-water selectivity.On the basis of laboratory experiment and well performance, the oilfield trials of water shutoff for 6 horizontal wells have been carried out in Kunbei Oilfield. The remarkable effect of increasing oil and reducing water has been gained.