Abstract: Nickel production is a typical multi-element symbiotic smelting process, and inventory allocation is an important technical factor that restricts the accuracy of its life cycle assessment. In this study, the flash furnace smelting process of nickel sulfide ore with the most intensive symbiotic reaction was taken as the research object, and various inventory allocation methods such as system boundary extension, physical relationship and mass allocation were adopted to allocate CO₂ emissions among the three elements of Ni, Cu and S. The allocation calculation results by system boundary extension show that the allocation factor of non-metallic symbiotic elements is 29.86%, and the allocation factor of metal symbiotic elements is 70.14%. The results show that the system boundary extension method is not suitable for intermediate products. The factor of physical relationship allocation are accurate, but need to be supported by a large number of process parameters. The mass allocation is easy to calculate, however, its accuracy depends on the differences of physical and chemical properties between symbiotic products.