This study is designed to investigate into the nature of syndrome differentiation as thinking activity.Methods:Targeted at the stream of consciousness of syndrome differentiation, a general rule was discovered with an overall point of view. Using such phenomenological Methods as reduction, synthesis, externalization, etc., a structure analysis of intentionality was applied to discover the features and significance of intentional behaviors.Results:Syndrome differentiation was an intentional behavior of prescribed nature that incorporated association, composite and integration; the intentionality, which was inevitably related to Chinese medicine’s content and pattern, permeated in the whole process of experience of symptoms, i.e. syndrome synthesis.Conclusion:Projecting priori analysis of the subjective side onto the understanding of the objective side is a new sustainable way of development for modern research of Chinese medicine theory.