The closed sump is a typical inlet passage of middle and small pumping station.It has the characteristics of low channel height, small foundation excavation depth, simple structure, a single cross sectional shape changes, ease of construction and other features, so more and more attention and application has been paying on this closed sump in pumping station project. However the flowing pattern within the closed sump is complex,the design is not perfect in some respects, the structure size does not be optimized. Based on the background for renewal and transformation of a pumping station,according to the three-dimensional incompressible fluid reynolds-averaged N-S equations,the RNG k-ε model,the CFD technology.The design criteria of geometric parameters of closed sump could be used in the project.The paper simulates the closed pump sump.The results are as follows:(1) Compared the calculation results of closed sump and the calculation results of open sump,analyzed the basic flow pattern,the pressure distribution,the velocity distribution in the sump and the flare,the plate could promote the performance of pump sets and change the flowing law of pump sump.(2) One factor method which changed one geometric parameter and constant the other three geometric parameters unchanged study the influence of hydraulic performance when the geometric parameters changed.Pump assembly efficiency changed small when the height of plate control in 0.5DL-0.9DL. Changed significantly lower when the height of plate at 1.1DL.When the height of plate is 0.9DL,the pump assembly efficiency is highest.The pump assembly efficiency increased when the width increase. The pump assembly efficiency reduced when the distance of back wall increase. When the distance of back wall achieve 0.6DL,the pump assembly efficiency changed small.The pump assembly efficiency increased when the floor clearance increase.0.25 to 0.5DLfast,after 0.5DL slow。(3) The flow pattern in close sump is complex,single factor method can’t comprehensively study the effect of hydraulic performance of the closed sump.This paper study the geometric parameters from another method called orthogonal test and compared the calculation results between the one factor method and the orthogonal test.Two methods reflected well regularity,so the methods and the calculations are reliable.This paper give the design criteria of geometric parameter of the closed sump through research the calculation results:the height of plate control in 0.8DL-1.0DL,the distance of back wall control in 0.3DL-0.6DL,the floor clearance control in 0.5DL-0.75DL,the width control in 2.7DL-3.2DL.Also give some parameter combination which possessed well pump assembly efficiency.(4)The unsteady flow calculation of a plan from the orthogonal test and a original plan give the pressure fluctuation in the closed sump when the impeller was rotating.The peak-to-peak value of P1 of the original plan is 0.052m,the peak-to-peak value of P1 of the optimization plan is 0.050m,the peak-to-peak value of P2 of the original plan is 0.038m,the peak-to-peak value of P2 of the optimization plan is 0.034m,the peak-to-peak value of P3 of the original plan is 0.039m,the peak-to-peak value of P3 of the optimization plan is 0.033m.The peak-to-peak value of optimization plan is smaller than the original plan.The peak-to-peak value of optimization plan account for head is 3.723%,2.532%,2.457%.They all small than 4% of head,so the flow of closed sump is stable.