Abstract: High collapsibility of loess appears in sorth part of Ningxia. The research result show that the loess collapsibility is causted by pore microstructre, and close relation between granula metrical composition and cement types. Other factors affecting loess collapsibility are soil thickness permeability coefficient, and occurence depth. Other properties of loess are also explained herein. We obtain the detail information of the soil formed in different processes and environments. From these result we suggest a collapsibility mechnism of loess. Finaly some Measures to prevent and control loess deformation are discussed.