In this paper, the studies concerning ecosystem stability and niche were reviewed and analysed. On this basis, the theory of thermodynamic stability is introduced into the study of ecosystem. At an equilibrium state, the stability of ecosystem can be determined according to the behaviour of extrem value and development with time of entropy S; in the linear region of none-quilibrium it can be judged of from the entropy production P≥0 and dP/dt< 0; and in the nonlinear region of noneguilibruim super entropy d...