Abstract: Material separation is the core technology of many medical and industrial applications.Traditional solid filtration membranes can allow particles smaller than the critical size to pass through the membrane while blocking the passage of larger particles.However，membranes that allow large particles to pass through while small particles stay are difficult to make artificially.Stogin，Gockowski，et al (in Sci.Adv.2018，4:3276) proved that a liquid membrane composed entirely of liquid can be designed to retain particles smaller than the critical size and permeate largesize particles.Based on the above research，this article analyzes and derives based on the liquid membrane filter model，analyzes and discusses the critical permeability conditions of the liquid membrane，and is verified in the experiment.At the same time，this article realizes the screening of particle velocity by adjusting the surface tension coefficient of the liquid membrane.

Key words: liquid membrane filter, critical permeation condition, soap membrane