GA (genetic algorithm) is well known by the comparatively good ability to get solutions of various combination problems in a short time. Because optimal solution may not necessarily be obtained, expanded GA that has some operations in addition to fundamental GA operation is employed in this paper. This paper proposes a practical optimization method of structural planning of a lattice dome by GA. Four evaluation functions, i.e., cost of dome, deformation, buckling load of whole dome and that of structural members are employed in GA operation. Consequently, it is proved that approximate optimal solutions can be efficiently obtained in comparison with the calculation results of all combinations of given parameters.