Starting with the product structure design, the general evaluation index system of mechanical product structure design for assembly and the special evaluation index system for concrete product have been set up, meanwhile the fuzzy evaluation methods and procedure for product structure design were explored. Some techniques related with fuzzy evaluation of mechanical product structure design for assembly have been carried out, and knowledge representing form of combining frame with rule, establishing method of acquiring knowledge platform for evaluation-index by using Matlab, membership function determination method through reasoning, adopting the Delphi method for determining the steps of index weighing were all included in the techniques. Further more, a specific mechanical product was assessed and analyzed.