The pneumatic defogging system is applied to the separation of lubricating oil fog in large units, and the Venturi tube is the core component of the pneumatic defogging system. In order to study the performance of Venturi tube in pneumatic fog removal system, firstly the influence of inlet pressure, back pressure and tank size on pressure and heat transfer in Venturi tube was analyzed based on numerical calculation method, and the accuracy of numerical calculation method was verified through experiments. Then, the rule of negative pressure, temperature drop in Venturi tube and droplet size at outlet were studied experimentally. The results show that the greater the inlet pressure and the smaller the outlet back pressure, the greater the negative pressure of Venturi ejector tube. The main factors affecting the temperature drop of Venturi suction system are tank volume and ambient temperature. The larger the tank volume, the greater the temperature drop. The higher the ambient temperature, the higher the outlet temperature. At the diffuser section of Venturi tube, the agglomeration effect of droplets is greater than the breaking effect, and small droplets gather and form large droplets.