The present work introduces a numerical investigation of steam ejector optimum performance at constant pressure ratio used in many applications. The present study aims to maximize the ejector efficiency by optimizing the ejector mass ratio. The effect of geometrical parameters on ejector mass ratio and its efficiency is investigated at constant operating conditions. These parameters are the ejector convergent section angle, the constant area mixing chamber length and the angle of the ejector divergent section. The results showed that the ejector wall static pressure distributions were greatly affected by the investigated geometrical parameters. Furthermore, In order to avoid separation, the ejector divergent section angle must be selected carefully together with the operating conditions. The ejector mass ratio and efficiency increased with increasing the previously stated three geometrical parameters to gain their upper limit values, subsequent to that, the efficiency and mass ratio decreased with increasing these geometrical parameters. Moreover, there are certain optimum ejector convergent, divergent angles and the constant area mixing chamber length in order to optimize the ejector mass ratio and consequently its efficiency at given constant operating condition.