Problems such as complex variant process and the easiness of generating conflict of constraints existed in traditional variant design methodology. Aiming at the problem of the complexity of dependent relations among parts as well as configuration and variation in design process must be alternated and intervened by designer, a rapid variant design approach under design template frame was proposed. Taking advantage of flexibility and information carrier function of templates, concept of variable element was put forward. Rapid variation of artifacts was realized within definition domain of template through creation of interrelation among variable elements to relate parameters with each other. An example of gearbox of small agricultural machinery was used to verify that serialization through structural variation and diversification of product through changing the geometric parameters in same series.