The remediation and utilization of salt-affected soil through the application of green and sustainable technologies are important for cultivating healthy soil, ensuring global food security, and mitigating global climate change. Biochar has the potential to improve soil health and increase crop yield because of its multiple advantages, such as excellent pore structure, abundant surface functional groups, and high carbon stability. Recent research focusing on the improvement of salt-affected soils via biochar application has garnered increasing interest. However, the effect of biochar on salt-affected soil is extremely complex and diverse, resulting in a lack of critical mechanisms responsible for biochar performance in salt-affected soils. This greatly limits the application of biochar technology for the improvement of salt-affected soils and the industrialization of biochar. Therefore, this review comprehensively analyzed the impact of biochar on the physical, chemical, and biological properties of salt-affected soils. Specific focus areas included the relationship and critical mechanism between biochar properties and salt-affected soils and the deficiencies in areas that need to be strengthened. We emphasize the importance and urgency of comprehensively evaluating the effects of biochar application in the remediation of salt-affected soils from the perspective of soil health. In this study, we aimed to provide a theoretical basis for the application and popularization of biochar, as well as technical assurance for the green development of salt-affected soils.