In the cementing of deep and ultra-deep oil and gas wells，due to the influence of formation high temperature，some additives in cement slurry fail，which causes sedimentation of solid particle. As a result，the slurry loses stability and the risk of channeling increases in cementing process. Polyelectrolyte hydrophobically associating composite suspension stabilizer（P-AB）was prepared by strong electrostatic interaction between positive and negative ions using 2-acrylamide-methylpropanesulfonic acid， acrylamide，N-vinylpyrrolidone and N，N-dimethyloctadecylallyl ammonium chloride as raw materials. The structure of P-AB was characterized. Its influence on the performance of cement slurry was studied，and the suspension stability mechanism was analyzed. The results showed that P-AB could form a unique grid structure through electrostatic interaction and hydrophobic association， which helped to suspend cement particles and prevented cement slurry settlement and free water separation. At 40—150 ℃，1% P-AB aqueous solution could maintain high viscosity. After adding 0.5%—1% P-AB into cement slurry and curing at 200 ℃ for 1 d，the density difference between the upper and lower segments of cement stone was less than 0.02 g/cm³，and there was no free liquid of cement paste. P-AB mainly increased the settlement resistance of cement particle material through hydration，and formed a dense cross-linked network structure through electrostatic adsorption and hydrophobic association，which ensured the stability of cement at high temperature. This technology was conducive to improving the cementing quality of deep and ultra-deep wells and reducing the cementing risk.