It is obvious that product variation and customization have become the current trend to fulfill the customer requirements in severe competitive environment. However, how to manage the ever-increasing number of variant products becomes a critical challenge for enterprises. To address this problem, this research proposes a common module mining method to derive common modules from variant products. First, each product is decomposed into a set of single-level trees (SLTs). Then, SLT similarities in any pair of SLTs in the product database are derived. Finally, a mining algorithm is developed to generate common modules. A set of experiments are conducted to show the feasibility of the proposed method. These common modules are found so that similar production and maintain approaches can be applied. The result shows that the proposed method is a valuable tool to manage massive variant products.