In order to solve the problems of repetitive work, low design efficiency and difficulty in subsequent modification in the design procedure of framed-mold in autoclave processing for composites structures, the parametric design technology which is applied to the design of the mold, is divided into two aspects: the parametric design of dimensions and the parametric design of topological structures. In terms of parametric design of dimensions, based on the analysis of structural characteristics of the mold, the main design parameters of the mold are extracted, and the parametric design process is planned using the top-down design method. The concept of parameters tracing and the method of tracing main design parameters are proposed so as to modify the dimensions of the mold rapidly through parameters. In aspect of parametric design of topological structures, some topological structures of the mold can be modified parametrically by combining the knowledge engineering module of CATIA with object-oriented technology. Based on CATIA CAA secondary development platform, a parametric design system of mold in autoclave processing for composites structures is developed and verified with examples.