Abstract: The numerical simulations of bifurcation phenomena in a combustor with a non slot conical swirler and in a diffuser fixed before the non slot conical swirler have been carried out.The results of the simulations show that there are two different kinds of vortex emerged before the conical swirler,that may be one of the feed back factors controlling bifurcation phenomenon,and the characteristics of the turbulent flow in the combustion zone must be changed abruptly as the bifurcation phenomenon occurs.These conclusions may reveal the causation of bifurcation phenomenon in this combustor from the viewpoint of aerodynamics.The calculated results are consistent with the experimental data.