Abstract: In the drilling process of deep and ultra deep wells, nano-polymer plugging agent plays a crucial role in dealing with the borehole instability in the strata with developed micro pores and micro fractures, but the plugging agent of high molecular polymer type tends to suffer degradation failure under high temperature. A kind of nano-polymer plugging agent was synthesized by means of emulsion polymerization method by selecting N, N-dimethyl acrylamide (DMAM), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), styrene (ST) and diallyl dimethyl ammonium chloride (DMDAAC) as the reaction monomers, ammonium persulfate as the initiating agent and N, N-methylene-bis-acrylamide (MBA) as the crosslinking agent. Infrared spectrum shows that the synthesized material is the expected product and grain size analysis show that its median size is 129 nm. What’s more, its plugging capacity under high temperature was evaluated by means of sand bath plugging experiment, combined with API filtration and high temperature and high pressure (HTHP) filtration before and after the high temperature aging. After aging under the high temperature of 180 ℃, the drilling fluid with 1% nano-polymer plugging agent has API filtration of 24.4 mL, HTHP filtration of 92 mL and HTHP sand bath filtration of 66 mL. It is experimentally indicated that the optimization of molecular structure solves the problem that nano-polymer plugging agent is likely to degrade under high temperature and the synthesized nano-polymer plugging agent has strong temperature tolerance and plugging capacity.