New diffuser profiles designed by constant rate of velocity or pressure change method (CRVC／CRPC) were adopted to improve the jet pump performance. The orthogonal design was used to arrange the structure combinations of jet pump. The throat length, diffuser angle and profile were chosen and each factor had three levels. Considering the interactions between factors, 27 combinations were obtained and simulated to gain their performance. The effect of structure parameters on the flow details was studied. The results from the variance analysis show that all the factors and interactions have great influence on the pump performance. The interactions among the geometric parameters should be considered during jet pump optimization. The CRVC or CRPC diffuser produces a smoother and more uniform velocity and pressure gradient along the axis than the conical diffuser. Combining with appropriate throat length, the CRVC or CRPC diffuser could improve the pump performance and shorten the total pump length considerably. The most desirable combination consists of a throat with its length 6 times of its diameter and a conical diffuser with angle of 8°