Abstract: A novel mass-energy coupling treatment system for blast furnace slag was proposed, which realized efficient recovery of waste heat in slag and high value-added utilization of slag components. The methods of life cycle assessment and life cycle cost were adopted to calculate the environmental impact and economic cost of the system. The resource and energy consumption included were also calculated. Main sources in terms of environmental impact, economic cost and resource and energy consumption of the system were traced through the identification of main contributors. The key elements to system optimization were determined through the comprehensive performance evaluation and sensitivity analysis. Besides, the environmental, energy and economic benefits of the system were analyzed based on its characteristics. The results showed that: 1) The environmental impact of the system was mainly global warming (with a contribution rate of 47.68%), the economic cost was mainly internal cost (with a contribution rate of 91.89%), and the resource consumption was mainly non-energy resources (with a contribution rate of 98.57%). 2) The key unit to system optimization was pretreatment and the key input was HCl. 3) For each ton of slag treated, the net CO₂ emission was −6 098.68 kg, the net energy consumption was −682.68 MJ and the economic cost was 2 078.24 yuan after a full consideration of system characteristics.