In order to improve the temperature resistance and salt resistance of polyacrylamide oil displacement agent，the molecular structure design idea was adopted to design the polymer structure from the primary and secondary structures of the polymer，and the advanced structure and molecular chain aggregation state of the polymer were analyzed and integrated. Taking AM and AMPS as the main monomers，a random micro-branched/micro-crosslinking associating polymer was synthesized by introducing self-made hydrophobic monomer and branched monomer. The effects of AM/AMPS ratio，branched monomer dosage， hydrophobic monomer dosage，pH value and initiation temperature on the viscosity of the polymer were studied by orthogonal test， and the temperature resistance and salt resistance of the polymer were studied. The results showed that the order of the influence of various factors on polymer viscosity was as follows：branched monomer dosage ＞ hydrophobic monomer dosage ＞ AM/AMPS molar ratio ＞ pH value ＞ initiation temperature. When the molar ratio of AM to AMPS was 5∶1，the amount of branched monomer was 0.5‰，the amount of hydrophobic monomer was 1‰，pH value of the system was 7，and the initiation temperature was 2 ℃，the obtained polymer had the highest viscosity. The synthesized random micro-branched/micro-crosslinking associative polymer had high intrinsic viscosity of 2 868 mL/g，lower insoluble content of 0.12%，higher polymer viscosity and better thermal stability. The viscosity of the polymer solution with the concentration of 1 500 mg/L was 12.8 mPa·s after aging for 180 d at high temperature of 95 ℃ and at salinity of 40 000 mg/L，and the viscosity retention rate could reach more than 85%. After aging，the random micro-branched/micro-crosslinked association polymer solution could still meet the viscosity requirements of oil displacement agents，and the polymer solution had excellent long-term stability in the formation.