The recycling of waste polyethylene terephthalate (PET) is widely regarded as an eco-friendly and cost-effective technology and has been gradually developed into an important direction for the utilization of solid waste resources. However, the integrated evaluation research on this technology from the environmental, economic, and social aspects are still not in place. Based on the theory of collaborative entropy, this study constructs an integrated evaluation and optimization methodology system for the environmental, economic, and social impacts of blanket production from recycled PET, using environmental life cycle assessment, life cycle cost assessment, social life cycle assessment, and sensitivity analysis. The study assessed the environmental load, economic cost, and social impact of blanket production from recycled PET, and then identified the key processes through sensitivity analysis. In addition, the graphical method and the principle of collaborative entropy model are applied to evaluate two of the environmental load, economic cost, and social impact in the blanket production from recycled PET. The results of the two methods are consistent, which indicates that to carry out multi-objective integrated evaluation with collaborative entropy model have good reliability. Moreover, the quantified results of collaborative entropy showed that the key processes that affected the coordinated development of the environment, economy, and society were organic chemicals usage process, electricity generation process, and direct air emission process. Based on the "Reduce-Reuse-Recycle" theory and the position of key processes in the system, feasible optimization suggestions were proposed. The establishment of this methodology system could provide theoretical and practical references for other waste utilization industry.