Two-dimensional numerical simulations were carried out to investigate the effects of the shape of mixing chamber on the performance of annular jet pumps for several jet flow rates. We confined the computational domain to a jet, a mixing chamber, and the outlet of the pump. Several computations have been carried out to seek the effects of reducing angles on the suction performance and the efficiency of the jet pump. Some numerical results regarding suction flow rates, head ratios, the efficiencies of the pump, flow fields and pressure distributions are shown and discussed.