Abstract: A type of water soluble polymer is synthesized by solution copolymerization of acrylic acid (AA), acrylamide (AM), and acryloyloxyethyl trimethyl ammonium chloride (AETMAC) with ammonium persulfate as the initiator. The impact of temperature and salinity on the reduced viscosity of the polymer solution is investigated. The temperature and salinity stabilities of the polymeric drilling fluids are tested. The filter cake morphology is characterized by Scanning Electron Microscope(SEM). The results indicate that the filter loss of the polymeric drilling fluids reaches minimum with 20% as the concentration of AETMAC, whereas it would be increased if the AETMAC concentration gets too low or too high. The filter loss of the polymeric drilling fluids would increase slightly with the increase of salinity or temperature. The result of SEM shows that the filter cake has many holes which are irregular, compact, and micron-sized.