Shipright is a very important and skillful work to maintain ship quality well and to improve the productivity of shipbuilding. Though this work now depends on skilled workers in the shipyards, they become aged and will soon retire, and the training of their successors or other countermeasures/system are required. Recently, CAD system and product model of CIM have been applied widely, and also efficient measurement technology has developed in shipyard, then it becomes possible to apply a positional control in erection stage. This report presents a computer simulation method to put a block, which has dimensional errors, on the suitable position as designed using genetic algorithm (GA). A pilot program of “C” using personal computer has been developed and applied for a typical hexahedron block. The simulation results showed a good solution to get optimum position.