The development of low-carbon technologies is one of the essential pieces to achieve carbon peak and carbon neutrality in Chi⁃na. However, from a life-cycle perspective, the industrial application of new technologies also requires additional resource inputs andbrings new emissions, and the carbon reduction effect is uncertain. Thus, life cycle assessment (LCA) is needed to quantify the contribu⁃tion of all unit processes to the carbon footprint, and to guide the process design and optimization of low-carbon technologies. For the con⁃ventional LCA, the environmental impacts are ex-post evaluated based on the industrial-scale production system, but it is difficult to ob⁃tain the data required for LCA for technologies that are still being developed at a pilot scale. Therefore, to evaluate the potential life-cycleenvironmental impacts of a technology under lab-scale development, the methodology development for ex-ante LCA will be a vital topic inthe field of industrial ecology. At first, the main issues about the methodology of ex-ante LCA were summarized, including the difficultyof modeling the inventory data, defining the system boundary, and result interpretation. In addition to the application of the ex-anteLCA method to roughly estimate the potential carbon footprint and other environmental impacts of new technologies, it Is proposed thata more important function is to identify and optimize processes with high environmental impacts by quantifying the current carbon footprintof industrial ecosystems related to new technologies as a baseline target for the research and development of new technologies, so as to makelow-carbon design recommendations for industrial applications. By summarizing representative cases of ex-ante LCA of emerging technolo⁃gies, it is found that there is an order of magnitude gap between the carbon footprint calculated based on pilot-scale data and the actual in⁃dustrial scale, so it is recommended to invest a small amount of additional manpower and software and hardware resources in the research anddevelopment process to realize the amplified simulation of the process, predict the energy consumption and input/ output lists of the industrialscale, and carry out the life-cycle environmental impact assessment. Finally, as a case study for guiding the low-carbon development oftechnologies, the green design of a Cl recovery process for PVC waste was revealed by the integration of experiment, simulation, and ex-anteLCA for quantifying the influence of process variables such as different reactant concentrations, treatment volumes, reactor designs, operat⁃ing conditions and other process variables on the list of process inputs and outputs, such as consumption of energy and raw and auxiliary ma⁃terials, direct emissions, product yields, and the amount of wastes generated. Meanwhile, it realizes the use of carbon footprint as an evalua⁃tion indicator to guide the research and development of low-carbon process design and operating conditions for new technologies.