Abstract: The flexible air-chamber jig is a novel coal cleaning machine.The airbag body of the jig is liable to break down due to fatigue damage under the effect of alternate differential loading during its operation.In order to determine the points at which the fatigue damage occurs during the process of expansion deformation of the airbag, the finite-element calculation method is used to establish the geometric model of the airbag and the mesh pattern.The fluid-solid coupling calculation method is applied to explore the law governing the distribution of stress and strain to which the wall of the airbag is subjected, and define the critical zones severely affected by expansion deformation of the airbag.Study result shows the stress and strain of the side wall along the axial direction both follow the pattern of first going up and then declining; the pressure difference and air-intake time at the boundary of the airbag are the key factors affecting the distribution of stress and strain; a maximum stress of 130 kPa is seen to occur at the middle part of the wall of the airbag, and a maximum strain of 1.159 appears on the bag’s wall at a point of Y=1.15 m along the axial direction of the bag—a point with a maximum deformation and also an area more liable to suffer fatigue damage; the strains of both sidewalls of the airbag assume a similar distribution pattern with their amplitudes being close to each other, indicating that the airbag undergoes an even and stable expansion deformation.The study made provides a new train of thought on the fatigue design of the airbag and also a valuable reference for coal preparation plants to extend service life of airbag and ensure safety of coal cleaning operation.