Abstract: On the bases of ventilation, heat-dispersion and dust-removal technology using engine exhaust gas energy, a kind of exhaust ejector has been properly designed with the consideration of the limitation of cabin space. On the ground of fluid dynamics theory, numerical simulation for the ejector is performed to obtain the relationship of injection coefficient with its key structure parameters. Having the designed prototype, different types of ejectors with different parameters can be tested to improve the injection capability. It should be considered that, according to the requests of compaction and lightweight, the maximal ejection coefficient is not the best design, but the adequate coefficient is good. Finally, the comparison of tested designed types indicates that ejector may have the most superior injection effect when chamber working segment is about 125mm long.