99-20E

A perturbation theory scheme in terms of electron hopping which is based on the Wick's theorem for Hubbard operators is developed. Diagrammatic series contain single-site vertices connected by hopping lines and it is shown that for each vertice the problem splits into the subspaces with "vacuum states" determined by the diagonal Hubbard operators and only excitations around these "vacuum states" are allowed. The rules to construct diagrams are proposed. In the limit of infinite spatial dimensions the total auxiliary single-site problem exactly splits into subspaces which allows to build an analytical thermodynamically consistent approach for Hubbard model. Some analytical results are given for simple approximations when 2-pole and 4-pole structure for Green's function is obtained.