Abstract: In this paper, δ-function is used to construct the generalized biharmonicoperators, the corresponding quadratic function is presented, and the latter is appliedto the bending of elastic thin plates, The result shows that when the arguments in the variational functional are generalized functions, discontinuity to sone degreeis allowed, and the modified variational principle by using the Lagrange multipliers is merely a special form of the result mentioned above.