Abstract: The divergence angle of a diffuser is one of the important structure parameters of the jet pumps,which has effect on the performance,interior flow field distribution and manufacture cost of the jet pump.In this paper,SIMPLE arithmetic and Realizable k-ε turbulence model is adopted to simulate the flow field and performance of jet pump of various divergence angles.The analysis on the centerline velocity,wall pressure distributions as well as the momentum correction coefficient and dynamic energy correction coefficient in the inlet and outlet of diffuser indicate that the divergence angle has less effect on the flow upstream the diffuser.It influences greatly the flow in the diffuser and downstream pipe.The effect of divergence angle on the performance and efficiency of jet pump is imposed by the resistance loss in the diffuser.Both the manufacture cost and pump efficiency should be considered together in the optimization of the divergence angle.Under a guideline of relatively changing 2.5% from the maximum efficiency point,the optimal divergence angle is proposed as 8°-11° considering the overall dimension and manufacture cost.