Taking polyhedral oligomeric silsesquioxane （POSS） as the organic/inorganic hybrid components and acrylamide （AM），2-acrylamide-2 methyl propyl sulfonic acid（AMPS），octadecyl dimethyl allyl ammonium chloride as monomers，a kind of organic/inorganic composite fluid loss additive PADD was prepared by emulsion polymerization method. The temperature tolerance and calcium resistance properties of PADD in bentonite slurry were analyzed. The results showed that the POSS compound in PAAD had good compatibility with the polymer matrix，and could form a cross-network structure in aqueous solution. The thermal decomposition temperature of PAAD exceeded 300 ℃，and the viscosity of the PAAD aqueous solution still was higher at the temperature of 200 ℃. PAAD had the effect of increasing viscosity and reducing fluid loss in bentonite slurry. After hot-rolling at the temperature of 150 ℃ for 16 h，2.0% PAAD could reduce the fluid loss of bentonite slurry contaminated by 10% CaCl₂ from 150 mL to 15.4 mL，thereby forming a dense filter cake. Microstructure analysis showed that PAAD could effectively shield the adverse effect of high temperature and high calcium on bentonite particles，which could maintain the dispersion stability of bentonite. The research prospect of POSS particles is broad，and the effect of modified POSS particles on the high temperature resistance of polymers should be further explored in the future.