Abstract:  In this paper，a class of chemostat systems with simulate seasons Environment in the following form ...  is discussed．It is abstained that the system has not periodic solution when b＝0；if b≠0 and b≪1 then system has 2π-periodic solution of system．globally asymptotically stable as m/Q＜μ*^－1 and is unstable as m/Q＞μ*^－1 and there exists at last one minimal 2π-periodic solution （ s（ t） ，x （ t） ） with x （ t） ＞0，0＜s（ t） ＜s*（ t） ．

Key words: simulate seasons environment, periodic solution, quilitative analysis