A new method to evaluate the conceptual design of a mechanical system by means of a fiziy distance measure is proposed. Firstly, all the factors that constrain the conceptual design are established, and the hierarchical relationship among them k set up in terms of usabiliq, dynamic performance, and manufacturability. And then the evaluation criterions are proposed for all basic mechanical units. Secondly, the rating of various altematives for each unit under different criteria and the weights of dzflerent criteria are represented, assessed and computed using standard fuzzy arithmetics. Based on the factor trees, a three-level fizzy comprehensive evaluation model is set up, which is characterized by multi-factors, multihierarchy features, multi-experts involved as well as various constituent units. The concept of fuzzy distance measure is introduced to decide the final ranking of altematives using a proposed algorithm. Finally, an example is given to show the process of evaluation using dktance measure.