Conventional polymer gel used for conformance control suffers from unfavorable temperature resistance and salt tolerance. The gel strength and gel stability decrease significantly under high temperature and high salinity conditions. A polymer gel system with temperature-resistance and salt tolerance prepared by formation produced water was developed based on polymer TSRP and phenolic resin crosslinker. The mechanism of thermal stability of the gel system was studied through Fourier transform infrared spectroscopy，scanning electron microscope and dynamic light scattering. The results showed that the gelation kinetics of the gel system was significantly affected by polymer concentration，the mass ratio of polymer to crosslinker，and the dosage of thermal stabilizer. The optimum formula of weak gel was obtained as follows：2 g/L polymer，1∶1 the ratio of polymer and crosslinker and 400 mg/L thioureas. When the weak gel was prepared by formation produced water with a salinity of about 38 g/L，the gel forming time was 63 h，and the viscosity of gel was 1760 mPa·s at 90 ℃ and 7.34 s^-1 . The gel system remained stable after aging 90 d at 90 ℃ . The good stability of the gel system at high temperature was related to two aspects. The ring structure of N-vinyl pyrrolidone in the polymer chain of TSRP improved the rigidity of the polymer chain，which effectively inhibited the thermal degradation of polymer chains. Besides，the rigid network structure formed by crosslinked TSRP could partly inhibit the curling of polymer chains at high salinity，which prevented the polymer gel from syneresis.