Abstract: To improve the performance of the annular slot ejector for gas dilution, the flow field of the WX-80 annular slotted gas dilution was numerically simulated using Fluent numerical simulation software for optimizing the ejector structure size and revealing the influence of mainstream pressure, throat gap and stagnation pressure ratio on its performance. The results shows that the mainstream mass flow continues to increase with the increase of the mainstream pressure, while the secondary flow mass flow and the ejector coefficient both increase and then decrease with the change of the mainstream pressure, and when the mainstream pressure is under 0.45 MPa, the secondary flow mass flow reaches the maximum value, that when the width of throat gap is between 0.1 mm and 0.4 mm, the mainstream mass flow is positively correlated with the throat gap, while the secondary flow mass flow shows a trend of increasing first and then decreasing. When the throat width is 0.2 mm, the rate of change of the ejector coefficient is the fastest. Within a certain range, the ejector coefficient decreases as the ratio of stagnation pressure increases.