The similarity theory and similarity criterion are applied to the series design of non-standard mechanical products. The series design method has been developed by using series design criterion; the similarity criterion of mechanical components or systems is transformed into the series design criterion of product. The series design method of mechanical product is more scientific and faster. The series design criterion is established for the single part of the non-standard mechanical product, and then is extended to the single and complex mechanical system. The series design method with main system and main parameter is put forward, and it is valuable for the complex mechanical system. The series design of rolling pulverization system is carried on by using this method, and the design criterions of the major parts in the system are given.