In the essay, the finite element algebraic equations by element assembling is replaced by node assembling, and the right term is dealt with by the idea of lumped mass, and the most compactly-stored finite element method is obtained.Thus, the total matrix elements are reduced to less than three times of unknown node, and the stored-units are even less than which the rectangle grid finite-difference method needs. The program structure is more rational and simpler, meanwhile the calculation quantity is reduced and the computational effciency is improded. All these become more obvious in process of solving nonlinear problems.