The jet pump is a device used for the entraining of a suction flow using a high-energy motive jet. The objective of jet-pump is achieved by three main parts: jet-nozzle, mixing chamber and a diffuser, the jet-pump performance is governed by geometrical parameters that shape these parts. In this study, the most crucial geometrical parameters that influence performance are investigated by an experimental and numerical parametric study, these parameters are mixing chamber relative length (Lr), motive nozzle relative spacing (S) and area ratio between the mixing chamber and the jet orifice (Ar). Besides the parametric study, the experimental work also provides the necessary data used to validate the numerical approach, which is concluded using 2-D simulation with transition Shear-Stress Transport (SST) as a turbulence model after showing very good agreement with the experimental data. Eventually, the numerical simulation is used to perform design optimization to specify the design that attains the optimum performance. According to the parametric study, it is found that area ratio has the most significant impact on the jet-pump performance and operating conditions, and the highest maximum efficiency of 35.8 % is obtained at pressure ratio of 0.28 and mass ratio of 1.25 for A_r = 4 using L_r of 7.3 and S of 0.785. While the optimum performance is found to be within optimum mass ratio range of (2.25 - 2.96) and maximum efficiency range of (32.5 - 29.4)%.