The tolerance information plays an important role on the quality uniformity and stability of the finished products. It should be kept in mind to maintain the tolerance continuity from initial product design to final product verification. Nowadays, customarized products are required to exchange their components to satisfy the individual customer’s demands and to accelerate the developing process simultaneously. The determinant factor for the exchangeability and components is the inter-component tolerance consideration. Especially, the critical tolerances of some key parts are the major factors to decide the uniformity of the product assembled. The objective of this study is to conduct a computer-aided tolerance analysis for the back light modules used in the liquid crystal panel. The tolerance allocation, analysis simulation functions and designated material characteristics are applied to each ingredient component. The simulation result can approach a reasonable set of tolerance design and allocation for each component under the prescribed limitation on the assembled components. The in-house allocation analysis software- RevCAD is used in this study. This simulation software is proved to be a powerful tool to increase the design efficiency and to improve the assembled product quality.