This paper presents a numerical study for predicting the steam ejector performance for different pressure ratios. The considered steam ejector operates at small pressure ratios of back to motive pressures. Both the suction and motive fluids are regarded to be dry steam. Due to low pressure created by the motive steam nozzle flow, entrainment of steam to be mixed with motive steam where both resume flowing toward the ejector exit. Mass ratio of suction to motive flows is an important element to describe the ejector performance.The present study aims to optimize the steam ejector efficiency that runs at different pressure ratio for each suction pressure. The variation of the mass ratio and ejector efficiency with the ejector back pressure at different values of the suction pressure and constant motive pressure, also a variation of the mass ratio and ejector efficiency with the ejector back pressure at different values of the motive pressure and constant suction pressure are investigated. The numerical results are validated with the available experiments from the literature. The results show that the mass ratio is almost constant at low values of back pressure, depending on the suction and back pressures, then the mass ratio decreases sharply with increasing the back pressure. The suction pressure has the positive consequence on the mass ratio. Moreover, the results show that the ejector efficiency increases with increasing the back pressure to gain its upper limit value, subsequently that the efficiency decreases with raising the back pressure. Also, raising the suction pressure will cause an improvement in the ejector efficiency. The value of back pressure at which the maximum efficiency is achieved and its value increases with magnifying the suction pressure.