To design the addendum efficiently and finely, a parametric method was taken to design section and then the addendum was divided into three portions, including surface adjacent to the part, transition surface and side wall, each of which was created by relevant method. The effect of the guideline production mode， construction of section and the method of the surface creating on the quality of the addendum was analyzed, a set of practical design process was summarized, and also a design module for addendum was developed on the UG platform based on a section base.