In this paper, the characteristics of low-rank coal for blast furnace injection after hydrothermal carbonization treatment was studied. The impact of the hydrochar injection on human health, energy, environment and other factors was discussed through the life cycle assessment method. Compared with pulverized coal injection, the hydrochar can improve the sustainability of the ecosystem and the healthy development of human beings. The impact on human health dropped from 24.61Pt to 23.73Pt, the ecosystem dropped from 0.53Pt to 0.51Pt, and the energy utilization rate dropped from 0.31Pt to 0.3Pt. Human carcinogenic toxicity, global warming, freshwater ecotoxicity and mineral resource scarcity are the most significant impacts. After using hydrochar, due to the increase of heat in front of the tuyere raceway and the improvement of pulverized coal utilization, the effects of optimizing coal gas flow distribution, improving reduction efficiency and strengthening smelting are achieved, thus reducing the impact of toxicity and greenhouse effect. Changes in freshwater ecotoxicity are mainly related to the sintering process and chemical reactions. The injection of hydrochar can make a positive contribution to the impact of ore resources. Moreover, the uncertainty analysis results show that the accuracy of the current model calculation can eliminate potential error risks. Thus, the application of hydrochar provides a better solution for the innovative, sustainable development and low-carbon production of iron-making process.