In order to maintain the harmony and stability of ecosystems,in this paper,the stability of Nicholson’s blowflies model with time delay was investigated.The distribution of the characteristic roots,the stability of the equilibrium,the existence of Hopf bifurcation and its conditions were discussed.Meanwhile,some simulations were carried out,which supported the theoretical results obtained previously and the global existence of Hopf bifurcation near the positive equilibrium point was got.At last,the reasons of circulating ecosystems were explained by the bifurcation theory.