A stochastic SIS epidemic model was analyzed,considering that the contact rate is influenced by environmental noise.The global existence,uniqueness and boundedness of its positive solution were proved by using the stopping time theory and Lyapunov analysis method.The stochastic asymptotical stablility of the disease-free equilibrium point was proved when the corresponding deterministic basic reproduction number is less than 1.It is also shown that the solution of the stochastic model oscillates around the corresponding deterministic endemic equilibrium point when the deterministic basic reproduction number is more than 1,and is of mean persistency when the deterministic basic reproduction number is more than 1 and the noise intensity is small.Besides,it is concluded that the large noise can make the disease extinct.Numerical simulations were carried out to prove the validity of theoretical results.