In the Shengli Oilfield，the temperature of ultra-high temperature reservoirs is 95-120 ℃. The existing polymer for oil displacement，after being placed at this temperature for 30 d，has a hydrolysis degree of about 100% and viscosity of only 1 mPa·s. Its oil displacement performance is greatly affected and cannot meet the polymer flooding requirements of this type of reservoirs. To improve the thermal stability and oil displacement performance of the polymer at ultra-high temperatures，we selected a new type of polymer with ultra-high temperature and hydrolysis resistance by introducing the AMPS and NVP monomer. We studied the performance of the polymer，including viscosity-increasing，rheology，injection and oil displacement，in ultra-high temperature reservoirs，and focused on the thermal stability of hydrolysis degree and viscosity of the polymer at 120 ℃. The results demonstrate that compared with conventional partially hydrolyzed polyacrylamide with similar relative molecular mass，the polymer in this paper has the more than doubled initial viscosity. With the viscoelastic performance greatly enhanced，it performs well in injection and oil displacement. After being placed at 120 ℃ for 30 d，it still has a hydrolysis degree of 0 and constant viscosity，indicating great thermal stability. It is promising to be applied to the ultra-high temperature reservoirs in the Shengli Oilfield，breaking through the temperature limit of EOR by chemical flooding.