In order to evaluate the assembly design plan reasonably and quickly, and ensure the excellent implementation of the assembly program, fuzzy evaluation method for assembly design was proposed. Firstly, the evaluation index system of assembly design was put forward on the basis of investigation and related literature search, the evaluation index was simplified, deleting the redundant indexes and retaining the necessary indexes with the aid of rough set theory and expert knowledge, and the quantification method of index was defined.Then, the importance of each evaluation index was analyzed, and the fuzzy weight of the comprehensive evaluation set was calculated. Finally, according to the property of the necessary index value and weight, the comprehensive evaluation of the feasible assembly design scheme was realized by applying technique for order preference by similarity to ideal solution,and the correctness of the method was proved by comparing with the evaluation results of fuzzy analytic hierarchy process and fuzzy comprehensive evaluation. An assembly sequence optimization process of a machine tool transmission system in an enterprise was quoted as an example to illustrate the feasibility of the proposed approach.The result shows that the fuzzy evaluation method of assembly design scheme is reasonable, and the optimized scheme has higher precision and efficiency.