Abstract: A DG85-80 five segmental centrifugal pump was chosen to work as a turbine and in order to obtain the external characteristics and the internal flow of the PAT, the numerical simulation of full passage in the case of PAT work with water phase and gas-liquid two-phase was conducted based on CFD software. N-S equations, the standard two equations κ-ε turbulent model, mixture model and SIMPLE algorithm were used for the simulation. The results indicated that at the optimum operating point, the head and power of gas-liquid two-phase turbine were higher than that of pure water turbine but the hydraulic efficiency and mass flow was lower. At the optimal operating point, with the series increase, the pressure difference of every impeller and guide vanes of turbine with gas-liquid two-phase media and the heterogeneity of its internal pressure distribution increased, while vortex region near the inlet pressure face of vanes was reduced. Compared with the turbine of the small flow, the GVF of every impeller and guide vanes of turbine with large flow was greater, the area of high GVF near the outlet of impeller was small and the asymmetry of gas distribution in each runner became exacerbated.