Abstract: The impact of the four major structural variables, including the throat diameter ratio, diffuser angle, throat length to diameter ratioand nozzle pitch, on the ejector coefficient of the steam-jet pump was mathematically formulated with regression model, theoretically analyzed inresponse surface method, numerically simulated with software Fluent and experimentally evaluated for design optimization. The results show that the structure significantly affects the ejector coefficient. For example, as the nozzle pitch decreases from 40 to 36 mm, the largest enhancement of the ejector coefficient decreases from 40% to 36%. The structure of the steam-jet pump, optimized with Design Expert software, comprises a throat diameter ratio of 0. 11, a diffuser angle of 8. 75°, a throat length to diameter ratio of 3 and a nozzle pitch of 36 mm. We suggest that the simulated and calculated results be of some technological interest in design optimization of steam-jet pumps.