A new approach of parametric design was named Variational design, which has high efficiency in structure design modifications consisting of simple elements such as points, straight lines and arcs. The article mainly introduced VDS modules in CCD. VDS provides the ability to assign parametric constraints to geometric ele-ments. By defining the parameters and calculating equation and constraints, the drawings in different views can be co-variation with dimensions changing. There was also a case of the bio-reaction tank design with VDS to illustrate the function of Variational design and CCD in details.