From the perspective of collateral disease theory, we expounded the correlation between the theory and cognitive dysfunction. Centering on the basic therapeutic principle of “unblocking collaterals”, we discussed the pathological mechanism of cognitive dysfunction regarding toxic damage to brain collaterals, phlegm and blood stasis, kidney deficiency and marrow reduction. In view of the above pathogenesis, the treatment methods such as detoxicating and unblocking collaterals, resolving phlegm and removing blood stasis, tonifying the kidney and activating the marrow were introduced respectively. In this review, we gradually clarified the ideas and methods for understanding and diagnosing cognitive dysfunction based on collateral disease theory, and provided TCM ideas for its pathogenesis, diagnosis and treatment.