An analysis method for commonality of module & part in modular product family was put forward. The part and module commonality in module layer and component part layer of product family were identified, respectively. The formulations of the two commonalities take into account amount of component part or module, variety, volume, price/cost of the part or module, size, geometry, material, manufacturing process, assembly. According to the source of parts, the mathematical formulas of self-made parts and purchased parts were set up respectively in the component part layer. Finally, an example of drive axle of wheel loader was given to indicate the effectiveness of the proposed method.