Aiming at the failure of existing fluid loss agent in the environment of high temperature and high salinity，a polymer microsphere was synthesized through inverse emulsion polymerization by water-soluble monomers，such as sodium p-styrene sulfonate with benzene ring structure and sulfonic acid group，2-acrylamide-2-methylpropanesulfonic acid and acrylamide，and oil phases，such as sorbitan fatty acid ester（Span 80），polyoxyethylene sorbitan monostearate（Tween 60）and liquid paraffin. Infrared spectroscopy，thermogravimetric analysis，scanning electron microscope and laser particle size analyzer were used to characterize the product. Then the swelling performance，salt resistance，aging performance，temperature resistance and plugging performance in the core were studied. The results showed that the microspheres displayed a spherical morphology with a particle size of 2.82—10.26 μm，and began to decompose at 270 ℃. It was found that the final expansion ratio of microspheres in deionized water was nearly 5 times the size of the previous one after reaching the swelling equilibrium. Microspheres exhibited a good fluid loss reduction performance in high salinity and high temperature conditions，and had good anti-aging property. A good plugging performance was observed in core plugging experiments. The polymer microspheres aggregated in macropores，where effective plugging was achieved.