Abstract: Numerical simulation was carried out for inside and outside flowfields of the liner in a small direct-flow combustor with special structural arrangement,numerical tests of combustor performance were performed for matching of different diffusers with the liner.The program employs two-equations(K-ε model)to describe turbulent characteristics.The combustion following vaporization was simulated by a two-step chemical reaction eombustion model.Arrhenius-EBU model was used to determine the reaction rate,and the air flow mass distribution was taken as a bridge to link the inside and outside flowfields of the liner.The calculated results indicated that two strong recirculation zones emerged when air flowed into combustor annular cavity from prediffuser,the inside and outside flowfields were very unsymmetrical.The inclination of the predliffuser was an important geometrical parameter for the combustor performance.