Finite element programming for three-dimensional convection diffusion problems is described. the classes of finite element models for convection diffusion problems are designed in C++. There are vector classes, matrix classes, element classes, material classes and method classes of finite element. On the basis of these classes, an object-oriented finite element program for three-dimensional convection diffusion problems is accomplished, which is able to simulate similar problems. it can also be applied to a large universal computational software for science and engineering.