Abstract: Non-uniform loading is one of the important causes leading to casing damage in unconsolidated sandstone reservoir with severely sanding production.Considering the characteristics of non-uniform loading,this paper has established three mechanical models of casing fit for the wells with severely sanding production under non-uniform loading(such as elliptical loading,diametral concentrated loading and orthogonal diametral concentrated loading),and based on the elastic theory,the formula that can calculate casing collapsing strength under the non-uniform loading has been obtained,which can help to study casing collapsing in unconsolidated sandstone reservoir.Research shows that the casing collapsing strength under non-uniform loading is far less than that given by API,and is about 3%~25% of that under uniform loading.Among the three mechanical models,casing can be collapsed most easily under diametral concentrated loading.Also,casing collapsing strength increases with the decrease of nonuniform degree of elliptical loading.