Flue collector of master-slave mode discharging system in domicile kitchen can be taken as one dimensional vertical steady flow with friction. By calculation of the distributional condition of the physical parameter of mobile phase and particle phase of flow, it can ascertain the flow condition of particle phase and further decide the discharging condition of fume. And it is affected by some conditions, such as highness of discharging system, diameter of flue and composition of material and so on. Through presetting the highness of discharging system and ensuring a well discharging condition, the diameter of master flue can be got to fit the condition. So a better size of cross section can be found for pipe laying, which both meets the discharging condition of fume aiwl economizes the construction material.