Because finite set contains limited subsets, it has many properties infinite set doesn’t have. This paper begins with the sum of all elements of subsets with k elements in finite set with n elements, gains calculating formula for Sn,the sum of all elements of subsets in finite set with n elements, and gets calculating formula for Sn,k(k=0,1,2,…,n), the sum of all elements of subsets with k order as well as unimodal nature and some other inferences.