Abstract: Hybrid life cycle assessment (HLCA) is an integration of process-based life cycle assessment (PLCA) and economic input-output life cycle assessment (EIO-LCA). This method expands the system boundary and supplements the environmental impact of the abandonment and use phases, thus solving the limitations caused by using one of these methods alone. Here, we introduce four HLCA methods and their advantages and disadvantages. Firstly, the hierarchical hybrid life cycle assessment method (tiered hybrid LCA, TH LCA) is easy to use, and the results cover a wide range, but with doubling-counting. Secondly, the system boundary of I-O based hybrid LCA (IOH LCA) is improved by input-output list, but lacks of the comparison analysis, because all the products in the same economic department are shown with the same factors. It usually results in inaccuracy issues. Thirdly, path exchange hybrid life cycle assessment method (PXC) replaces some paths with process data, which reduces repeated calculation results, but the calculation process is complex and difficult to use. Fourthly, there are two forms of integrated hybrid LCA (IH LCA), namely four-part matrix and nine-part matrix. The four-part matrix is the earliest proposed integrated hybrid life cycle method. It integrates the input-output table and process data into one matrix, which increases the difficulty of calculation but improves the accuracy of the results. The nine-part matrix retains the four-part matrix and adds the whole regional industrial chain database to analyze the environmental impact of the whole life cycle in different regions and different scenarios. By summarizing the life cycle assessment of TH LCA, IOH LCA, PXC and IH LCA, this review provides reference for the development and application of HLCA method.

Key words: hybrid life cycle assessment, process life cycle, input-output LCA, tiered hybrid, integrated hybrid