This paper deals with process design for mix-production line. First, we discuss issues of process line for mix-production and propose a method of process design for mix production to enhance productivity. The process design is treated as multi-objective problem in the method. Combination method of multi-objective genetic algorithm and clustering method is developed to design process line. Clustering method is utilized to generate groups of similar works with regard to connection relationship of parts in BOM and precedence relationship between works. We consider that quality of operation can be promoted and operation time can be reduced by assigning the groups of works to work centers. The developed method is performed on simple model to evaluate the performance of the method. The numerical experiments show that the number of clusters predetermined in the process of clustering is significantly affected to productivity of the line.