Abstract: Virtual assembly process was generally expressed with assembly sequence. However,the crossing assembly operations and installation adjustment can not be supported well by the method. By taking into account the actual assembly process planning requirements in design and manufacturing phases,a virtual assembly process information model based on assembly tasks is established. A hierarchical assembly process is employed to express the virtual assembly process. The crossing procedure and installation adjustment are realized through the strategy of crossing assembly of task target and given herein. A method to cut down the redundant assembly tasks is proposed. At last,the correctness and effectiveness are verified.