In order to reduce the effect of fluid loss reducer on the viscosity of drilling fluid，polymer fluid loss reducer GZ-1 was synthesized by four kinds of monomer，including acrylamide （AM），N-vinyl pyrrolidone （NVP），2-acrylamido-2-methyl propanesulfonic acid（AMPS）and allyl polyethylene glycol（APEG）. The molecular structure of GZ-1 was detected by infrared spectroscopy. The effect of GZ-1 on the rheological and filtration properties of drilling fluid was studied，and that on the microstructure of mud filter cake was analyzed by environmental scanning electron microscope. The results showed that the product accorded with the design. The viscosity-average molecular weight of GZ-1 was about 2.29×10⁵，and the viscosity was only 7 mPa·s when the concentration of GZ-1 was 1.6% in aqueous solution. With increasing concentration of GZ-1，the filtration loss of polymer drilling fluid decreased，the apparent viscosity（AV）and plastic viscosity（PV）increased modestly. When 1.6% GZ-1 was added in base mud，the AV and PV increased by 1.7 and 1.5 times as original mud，while AV and PV increased by 1.1 and 2.7 times after aging 16 h at 180℃. Even after the addition of barite to raise density，the viscosity of drilling fluid did not appear sharp increase. GZ-1 could make the mud filter cake more compact and inhibit coalescence of clay particle. GZ-1 had good resistance of high temperature（180℃）and had little effect on the viscosity of drilling fluid. The viscosity increasing effect of GZ-1 was less than that of common fluid loss reducer JT888 and SY-3.