Abstract: On the basis of the functions of faults in extensional structural deformation,the Cenozoic extensional structural system in the Weibei area,Shaanxi,is classified into the extensional fault set,propagational fault set and detachment fault set.On calculation,the cumulative horizontal extension amount of the study area in the Cenozoic is about 2.5 to 3.5 km,reflecting a situation of lateral extension of the area.The three sets of fault combine to form a model of extensional structure.