In order to analyses the effect of structure of collection loop on two-phase flow field in quenching furnace, the complex flow field in furnace for mixture of Nitrogen and spray water ejecting quenching under normal pressure and high velocity is numerically simulated with Mixture model of two-phase flow by CFD software FLUENT. Different inlet velocity, different volume percent of spray water, different velocity differences between Nitrogen and spray water, and different angle and dimension of collection loop affected on outlet velocity are analyzed. The research results show that the flow field is really complex, and around inner and outside canister and collection loop back flow exists. The angle of collection loop has less effect on outlet velocity, and the inner diameter of collection loop has more effect on outlet velocity. The simulation results show that the furnace can accelerate the flow of quenching media, which can cool specimen quickly.