Assembly is a classic discrete production, and assembly process is a flow of assembly state transition which is driven by assembly task. A new method, based on matrix technique, is presented to be used to model the assembly process. By adopting the new method, elements of assembly process such as assembly task, assembly state and assembly precedence relations are shown as matrix, and the assembly process is represented by the process of matrix calculation, which includes testing of the assembly task′s operability, assembly state transition, update of assembly precedence relations and so on. Because of the hierarchy of production structure, the assembly process can also be segmented into several sub assembly processes that are reflected on block matrix, and then the assembly process modeling with hierarchy is established. The feasible assembly sequence is obtained from the process which is expressed by matrix, providing the basis for the optimization of assembly sequence.