Abstract: Experimental data shows that the pores 0.02 and 0.08mm in diameter built on stilts are the main factor causing extreme intense and intense collapsibility, support pores 0.008 and 0.02mm in diameter are main factor carusing moderate and weak collapsibility.The different combinaction of pores results in different grades of loess collapse,the con spicuous characteristics of loess of extreme intense and intense collasibility are that the pores built on stilts occur in the form of meshes.The reduced amount of pores after collape is between 0.8-20%.Macropores also behave collapsibility to a certain extent,the collasibility of loess was formed in the porcess of soil forming in arid and semiaridareas.