<p>Due to unique technical and economic features, ejectors are widely used in various industries, including the water desalination industry and mixing fluids. Therefore, improving the ejector's performance is of utmost importance. In the present research, the effects of changing the primary nozzle outlet position (NXP) and changing the diameter of the primary nozzle (dn) on parameters such as Mach number, static pressure, dynamic pressure, mass flow rate, and entrainment ratio have been investigated and simulated using computational fluid dynamics. The results showed that increasing the NXP caused an increase in the mass flow rate of the secondary fluid and, as a result, the entrainment ratio of the ejector and a decrease in the size of the core of the primary fluid jet. This leads to an increase in the effective surface, a push of the shock train toward the constant-diameter region, and an increase in the maximum static pressure at the beginning of the diffuser. With the increase in the dn of the primary fluid jet core, the secondary fluid flow rate, the ejector entrainment, and the maximum static pressure value at the beginning of the diffuser increased, and the shock train was pushed toward the constant-diameter region.</p>