Abstract: The interior flow-field of jet pump was simulated by FLUENT and the effect of the nozzle-to-throat clearance,which is one of the most important structure parameters,on the performance of jet pumpwas analyzed.The characteristics of jet pump with two different area ratios were calculated under theconditions of different nozzle-to-throat clearances.Comparison between the efficiency curves of jet pumpswith various nozzle-to-throat clearances revealed that the maximum efficiency of the jet pump occurred whenthe nozzle-to-throat clearance is equal to the nozzle diameter.Under a guideline of declining 4% from themaximum efficiency point,the optimal scale of nozzle-to-throat clearance was found to locate between 0.5 to1.5 times of the nozzle diameter.