Abstract: Cognition encompasses essential mental processes, such as attention, memory, and emotion, which are fundamental to the way humans acquire and apply knowledge. With the rapid aging in the global population, cognitive impairments, including mild cognitive impairment, Alzheimer’s disease, and dementia, have emerged as significant public health concerns. The early diagnosis and effective treatment of these disorders are crucial for improving the quality of life of patients and reducing the societal burden associated with these conditions. However, traditional diagnostic and therapeutic methods, such as pharmacotherapy, functional magnetic resonance imaging (fMRI), and functional near-infrared spectroscopy (fNIRS), face several challenges, including low diagnostic accuracy, limited efficacy, and the lack of comprehensive assessment tools. The integration of brain–computer interface (BCI) and virtual reality (VR) technologies offers innovative solutions for cognitive diagnosis and treatment. BCI facilitates the exchange of information between the brain and external devices by analyzing brain signals, allowing for applications such as the rehabilitation of motor function disorders. Meanwhile, VR creates immersive and interactive environments that provide realistic experiences that can be used for cognitive training and rehabilitation. The combination of BCI and VR technologies enhances the effectiveness of cognitive interventions by providing multisensory stimulation and real-time feedback, making these interventions more engaging and potentially more effective. This paper reviews the current applications of BCI and VR technologies in cognitive diagnosis and treatment. Various BCI diagnostic methods based on Electroencephalogram (EEG), fMRI, and fNIRS, as well as VR-based diagnostic methods, will be introduced, and the advantages and limitations of these technologies will be discussed. In addition, this paper explores the contributions of cross-individual, cross-scenario, and cross-task EEG signal analysis to the precision and effectiveness of cognitive impairment assessment. The review will highlight the significant potential of BCI‒VR technology in various cognitive therapy domains, including cognitive behavioral therapy, memory and attention training, neurorehabilitation, and emotion regulation. The discussion will also tackle the challenges faced by BCI‒VR technology, such as device complexity, the need for personalized design, and the limitations of experimental samples. Despite the promising outlook for BCI‒VR technology, several challenges remain. The complexity of the devices, the lack of customization in virtual environments, and the adaptability of these systems across different individuals and scenarios are key issues that need to be addressed. This paper suggests that future research should focus on the miniaturization and cost reduction of BCI‒VR devices, the development of multimodal BCI systems, and the application of large language models to enhance the functionality and accessibility of these technologies. Furthermore, the importance of strengthening the collaboration among government, industry, academia, research institutions, and the medical field is emphasized as a critical factor in advancing the clinical translation of BCI‒VR technology for cognitive diagnosis and treatment. The review concludes that, although traditional methods have paved the way for understanding cognitive impairments, BCI‒VR technologies have the potential to revolutionize both the diagnosis and the treatment of these conditions. By overcoming the current technical challenges and fostering interdisciplinary cooperation, BCI‒VR systems can become integral tools in the global effort to improve cognitive health and enhance the lives of individuals who are affected by cognitive disorders.