Variant design has been recognized as an effective measure to implement mass customization. Assembly consists of different types of parts. Its variant design is a profound issue need to be explored. Three aspects were discussed in this paper, namely, 1) part classification and dimension constraint satisfaction priority, 2) part reuse, 3) dimension conflict and variant postponing. Firstly, dimension constraint network among parts was constructed based on graph. And variant dimension transferring was exploited. Secondly, reusable part can be found from existing parts through similarity analysis. Thirdly, aiming at dimension constraint conflicts, variant postponing was proposed to concentrate variant design to few parts so as to reduce the number of variant part.