Abstract: In order to find out the influence of throat area on the performance of tangent pump, CFD technology is used to five different throat diameter of tangent pump inside a three-dimensional unsteady flow numerical simulation to calculate the area of the throat different tangent flow pump in different operating conditions head and efficiency, to map out the flow head and efficiency curves for different speeds and finally flow conditions at the throat of comparative analysis of the causes flow cutoff value and flow coefficient. The study found that when a tangent pump throat diameter changes from 0.7D_d to 1.3D_d in its pump, head design conditions remain unchanged, and its scope become significantly larger; efficiency first increases with increasing flow rate and then decrease in the efficiency of the cut-off point near the maximum; lift cut-off point after the appearance of the head due to a sharp decline in the throat velocity is greater than the peripheral speed of the impeller diameter, and the sharp decrease in the peripheral speed of the impeller diameter, this results in a sharp decline in the head; tangent pump through a throat diameter of 0.85D_d, D_d, and 1.15D_d, flow coefficient becomes near the optimum efficiency and the flow coefficient of tangent pump should be appropriate in the 0.75-0.8.