Abstract: To resolve the problem of working volume reduction and environmental pollution caused by a large number of foams in fermentation, a type of environmentally friendly fermentation defoamer was proposed in this study. For the aim of pollution-free and high defoaming efficiency, a purely mechanical Laval structure was used for defoamer. Under the same working conditions, the inlet flow rate and negative pressure performance of the traditional spiral and Laval defoamer structures were compared through a three-dimensional conjugate finite volume simulation. The effects of the Laval structure parameter on the inlet flow rate and negative pressure performance of the Laval defoamer were investigated. Besides, ANSYS Workbench was used to analyze response surface (RS) and sensitivity to perform optimization. Results show that compared with the spiral deaerator, the average airflow velocity at the foam inlet of the defoamer with Laval as the core structure increases by 2-4 times. The inlet negative pressure increase by 57-599 Pa. The optimal throat radius of the Laval structure is 5 mm, the length of the compression section is 50 mm, and the length of the expansion section is 85 mm. The Laval defoamer is expected to promote low energy consumption and zero emissions in the bio-fermentation industry, and help achieve the "dual carbon" goal.