Abstract: A comparison of the classical displacement method with the classical force method is made. The classical algorithm of material nonlinearity problems, i.e. the step by step process based on the displacement method, is discussed and the unavoidable disadvantages of the step by step process are highlighted. A new method, called Large Increment Method (LIM), is introduced. It is based on the force method and the generalized inverse matrix (GIM) theory for material nonlinearity problems. Unlike the classical force method, the large increment method does not need primary structure any more, so this method imparts new life to the force method in computational mechanics field. The large increment method is different from the Large Time Increment Method (LATIN) presented by Ladeveze of University of Paris. GIM has some natural parallel-calculating characteristics which are different from the classical substructural algorithm. Some difficulties when applying the new method are overcome. The solution uniqueness and convergence of the method are proved. Only nonlinear elastic problem of truss systems is considered in this paper.