In terms of principle that similar parts have similar process, a measure method base on part's form similarity of feature is proposed. The form similarity measure of part is conducted in the similarity class of the whole feature. According to the layer of part's form information, the first stage of part form similarity measure is to match the maximal similar element of directional characteristics. The second stage of it is to measure the composite characteristics in the similar elements of directional characteristics. Finally, a comprehensive calculation of part form's similarity is made. The specific procedure of similarity measure is executed by the layer of part form feature information, which means different layers use different methods of similarity measure. By analyzing and defining the comparability of each layer, it matches the parallelism of each layer by the largest similarity degree from top to bottom and measures the parallelism of different layer' characteristics from bottom to top, and then use a case study of boxes parts to reveal the effectiveness of this methodology.