Aiming at the old oil fields with high temperature and high salinity，which cause more and more serious heterogeneity after long-term water flooding，Huabei oil field was taken as the research object. A hydrophobic polymer was developed by using acrylamide and acrylic acid as the main reaction monomers and introducing temperature and salt resistant monomer NVP and hydrophobic functional monomer，and a weak gel system with temperature and salt resistance was prepared through the crosslinking reaction between the polymer and the phenolic aldehyde resin crosslinking agent. The temperature and salt resistance，injectability plugging performance and fluid flow steering capacity of the weak gel system was measured. The results showed that when the concentration of polymer was 2000 mg/L，the polymerization cross ratio was 1∶1.5，the concentration of auxiliary agent amine persulfate was 2000 mg/L，the gel strength was higher than 1000 mPa·s at the reservoir temperature of 120 ℃ and the salinity of 37950.2 mg/L，moreover，the viscosity retention rate was more than 80% after aging for 90 days，which indicating that the weak gel had good temperature and salt resistance. It was observed that the micro network framework of weak gel after aging for 90 days was obvious，exhibiting good stability. The core flow test results showed that the weak gel system had good injectability. Under different permeability levels，the liquid flow diversion effect was obvious after the weak gel was blocked. The increase of the diversion rate of the low-permeability layer was as high as 48.33%，and the improvement ability of the water absorption profile was good. The sand filled pipe with different permeability was used for plugging，and the pressure measuring points of the sand filled pipe were pressurized in turn，the weak gel had good migration ability and the plugging rate was all over 85%.