In order to meet the demand of designing the waste gas efflux self-sucking device simply and practicably, based on the single-phase isentropic gas flow theory, a more effective theory analysis and design method was presented. The device’s main working parameters and characteristic indexes that had a signification effect in practice application were analyzed and given. And their calculating means were put forward. Some model was designed by this way and the parameters were analyzed by comparison with experiments. The result of the calculating case shows that the calculated data accord with the experimental data. And the method has good reliability with simpleness and practicality, which provides a good way of designing the self-sucking device.