Abstract: The rational finite element formulates directly in the physical domain and interpolates with the solutions, rather than using the iso parametric technique and interpolates with polynomials in the computational plane. Because of its analytical feature, the convergence can still be proved even if the element is incompatible. The present proof makes use of the method in applied mechanics, and is easier to be understood. The method can be extended to structures with multi types of elements. The convergence pr...