This paper presents a numerical method to simulate the collapse behaviours of unsaturated soils by distinct element method (DEM). The influence of suction in unsaturated soil is reproduced in DEM simulation by introducing an interparticle adhesive force that acts perpendicular to the tangential plane at contact point. A biaxial compression test on an assembly of circular rigid particles is numerically simulated using DEM by incorporating interparticle adhesive forces. The collapse behaviours of unsaturated soils during isotropic compression and biaxial shear are simulated by means of releasing the interparticle adhesive forces from the initially incorporated values to zero at constant stress state. The numerically simulated results are then compared with the results of triaxial compression tests on unsaturated compacted clays and qualitative similarities are obtained. The influences of the mean stress, the stress ratio and the interparticle adhesive force on the collapse behaviours are numerically investigated. The fabric structure and the particle stability of the simulated specimen before and after collapse are also investigated and discussed.