In the completion process of in-situ leaching borehole, the common gravel delivery equipments used at present are mainly slurry pump and non-subject gravel delivery devices. The gravel delivery device based on the ejector principle has wide range of field application, in order to improve its working efficiency and delivering quality, the optimization analysis is made on the numerical simulation of ejector structure of gravel delivery device based on the ejector principle by employing numerical simulation software Fluent based on computational fluid dynamics in this paper. The analysis results show that the diameter of the nozzle has great influence on the performance of the ejector and the injection coefficients of ejector decrease with the increase of ejector nozzle diameter, but the smaller nozzle diameter will lead to the increase of pump pressure load of mud pump. For BW250 mud pump used in the field site, the required maximum pressure is not greater than 6MPa, so the optimal nozzle diameter in the study is 5mm in this case. For the increase of the mixing chamber diameter will reduce the performance of the ejector, the optimal parameter is determined as 18mm based on gravel passing capacity and some factors; the appropriate increase of the length of mixing chamber is beneficial to improve the ejector performance, ideal length of 120mm is decided after optimization. The delivery efficiency and quality of optimized delivery device are greatly improved than those of original delivery device based on ejector with large diameter nozzle.