Recently agile manufacturing is strongly required to meet diversified customer orders and shorten product life cycle in the globally competitive market. This study aims for realizing new assembly process planning methodology. First, a concept of simplified assembly process planning composed of three characterized planning items is newly proposed by analyzing 20 actual assembly process. Next, a new assembly process planning model based on the unique new description method of the model is newly proposed to realize fast accurate assembly planning. Finally, the model is demonstrated the effectiveness by applying for the process planning of a blower in an auto air-conditioner.