In order to reveal the degradation of anionic polyacrylamide microsphere，anionic polyacrylamide P（AM-AMPS）microsphere was prepared by emulsion polymerization using 2-acrylamide-2-methylpropanesulfonic acid（AMPS）and acrylamide （AM）as monomers. The structure and thermal stability of the prepared microsphere were analyzed by transmission electron microscopy，infrared spectrometer and thermogravimetric analyzer. The viscosity，pH value and particle size of the microsphere which degraded different times at 80℃ after swelling in water were measured. The results showed that the synthesized P （AM-AMPS）microsphere had a uniform distribution with a particle size of about 70 nm，whose thermal stability was similar to that of linear polyacrylamide under anhydrous condition. Different from the linear polyacrylamide hydrolysis，whose hydrolysate was alkaline and the pH value slowly increased，the oxidative degradation of free radical caused the viscosity of the microsphere solution to drop sharply during 0—4 h microsphere degradation in solution，while the hydrolysis reaction was relatively slow，and the pH value maintained at about 2.75. After 4 h，the oxidation degradation rate of free radical decreased，and the hydrolysis reaction promoted the pH value of solution to rise rapidly. Within 0—4 h of the degradation reaction，the anionic polymer segment in outer layer of the microsphere degraded first，and then the microsphere core partially broken，and the particle size of the microsphere rapidly decreased.