Ensuring the environmental sustainability of products is challenging because it involves all the stages and processes throughout product life cycle. Product eco-design is essential to achieve it. In the proposed methodology, product eco-design is implemented based on five eco-design elements, namely, function, material, geometric structure, connection relationship and manufacturing process. However, because of the fragmentation of existing eco-design tools, the gap between eco-design evaluation and eco-design optimisation requires a new mechanism to seamlessly integrate them for efficient industrial applications. A new checklist tool called Checklist of Product Eco-design Optimisation Potential (CPEOP) is developed to assess product eco-design optimisation potential. Based on the new tool, optimisation effect of product eco-design can be quantitatively assessed. Furthermore, a novel semi-quantitative method for task planning in product eco-design is proposed, which involves evaluating the product with CPEOP, screening candidates for eco-design and determining the candidates’ optimisation directions. The uncertainties arising from CPEOP and enterprise design status quo are further analysed. Subsequently, a case study on a refrigerator is conducted to elucidate the process of the method and reveal its potential. The proposed method is then discussed through a comparison with two mainstream eco-design tools.