This paper proposes a correlational design method for the dimension tolerance and geometric tolerance of the feature of size when applying a material condition. Based on the equivalent transformation method, the calculation equation of virtual size and extreme virtual size for a single feature during free assembly is expanded to the calculation of those of related features at the datum positioning and directional assembly, and then the application rules of the material conditions are established. Two kinds of design requirements are considered: guaranteeing the distance requirement between the surface of a single feature of size and its datum, and guaranteeing the minimum clearance and minimum interference between two features of size. For these design requirements, the correlational equations for the design of the dimension tolerance and geometric tolerance are developed. Two design cases are conducted to demonstrate the design method.