As an important quality characteristic, maintainability is the ability of a product to be repaired efficiently and economically. Because it is mainly determined at the design stage, maintainability is mostly affected by the construction of a product. Traditional product design methods put more focus on design for function and production, neglecting design for maintainability, which causes a gap between functional construction design and maintainability design. The delay of maintainability design results in huge costs for design changes and even irrevocable design flaws. Because of the weak relationship between functional construction and maintainability in product design, the influence of maintainability design on the product is limited. To resolve this problem, this paper proposes a design approach considering the relationship between maintainability and functional construction. First, maintainability design factors (MDFs) and functional construction design factors (FCDFs) are defined and classified. Second, based on topology graphic theory, a correlative relationship model is constructed by graphically combining the MDFs and FCDFs into a network diagram. Third, to determine primary design factors, a quantization matrix is developed to perform importance evaluation of the correlative relationship. Finally, a practical case is studied by implementing the proposed approach for the lubrication system of an armoured vehicle. The results validate the effectiveness and feasibility of the approach.