Abstract: Under the actual environmental conditions, the use of variable geometry ejectors is an important way to improve the performance of ejectors. The effect of dimensionless nozzle distance on the performance and irreversibility of the ejector under different dimensionless throat lengths of the mixing chamber was studied by combining experimental and numerical analysis. The results show that in the test range, the critical entrainment ratio of the ejector first increases and then decreases with the increase of nozzle distance, and when the optimal dimensionless nozzle distance is 5.83, the critical entrainment ratio reaches a maximum value of 0.45. The critical condensation pressure of the ejector decreases gradually with the increase of nozzle distance. When the dimensionless throat length of the mixing chamber is 4, the critical condensation pressure decreases by 7.36%, and the decrease rate is the slowest. When the dimensionless throat length of the mixing chamber is 4 and the dimensionless nozzle distance is 5.83, the maximum thermodynamic perfection reaches 0.21. The entropy production of the ejector caused by the nozzle distance mainly comes from the mixing of the two inlet flows in the convergence section of the mixing chamber and the movement of the second shock wave towards the outlet of the diffuser chamber. Improving the pressure recovery ability of the diffuser can effectively avoid a sharp increase in entropy production. The results provide an important reference for the multi-objective optimization of the ejector structure and comprehensive performance to reduce the irreversibility of the ejector.