In this thesis, Environmental issues are considered as all harmful aspects of human activity on the biophysical environment. An increasing number of severe environmental issues () emerged in the last few decades leading Society to become more environmentally conscious. People are more concerned about the products’ environmental impacts and thus sales of environmentally friendly products have increased. In practice, the conventional life cycle assessment (LCA) is widely used by enterprises to reduce their product’s environmental impacts. It is a time-consuming method for enterprises, especially when the environmental burden shifting phenomenon is considered. In order to assess environmental impacts of different designs of products, the environmental emission data of each life cycle phase is required : so, when altering or improving a product, enterprises must recollect all materials-related data (existing product and waste produced). This limitation makes difficult for enterprises to quickly and accurately assess the environmental effects of their new product design. Unfortunately, even with the complex process involved, the LCA results do not completely reveal how to improve a product. The results can only help enterprises find out which materials or energy may bring serious environmental impacts, but they cannot help designers find out environmental friendly improvements or solution through design parameter modification easily. This thesis proposes a re-evaluation graph-based model to simulate the materials/energy variation in each life cycle phase after an environmentally friendly activity is taken. On the basis of the simulation results, the environmental emission coefficient is induced to convert the mass of materials/energy into the corresponding environmental emissions. This re-evaluation model can help enterprises assess the environmental impacts of their products more quickly. A sensitivity analysis approach is also proposed in this thesis. This approach focuses on the relations between environmental impacts and product design parameters. It is based on the LCA computation model with a parametric model to help designers choose proper design parameters to enhance the product’s environmental performance easily and quickly. Since the compliance to environmental friendly requirements is endless, enterprises need to improve the existing products’ environmental performance as much as they can. To achieve this objective, they can firstly use the re-evaluation model to assess the environmental impacts of an improved design. On the basis of the result, enterprises know the environmental effect of the improved design. Simultaneously, in order to estimate the applicability of the improved design, the re-evaluation model provides a decision making approach to help enterprise evaluate whether the design is applicable or not, i.e., if the effort sharing is distributed in an acceptable way for all companies involved in this product life cycle. In order to occupy more market, the product’s environmental performance needs continuous improvement. Enterprises can use the sensitivity analysis approach to find out which design parameter can improve more in product’s environmental performance. After finding out a new improved design, they can use the re-evaluation model again to check the effect of this new design. Thanks to the successive use of both methods, the product’s environmental performance can be enhanced continuously. In conclusion, the thesis focuses on continuous enhancing the product environmental performance. In order to achieve this objective, several main contributions are proposed, which include : a graph-based model considering the environmental burden shifting ; A decision making model considering environmental impacts and fairness of each company ; a sensitivity approach which can help designers to find out a new design to improve the product’’ environmental performance. More works will be done to overcome the limitations of the proposed models in future work, the remaining issues related to special tools devel.