OBJECTIVE: A method based on dubious condition of information entropy was introduced and applied to discuss a complexity problem in the analysis of correlation between traditional Chinese medicine (TCM) syndrome and season. METHODS: Eight hundred and seventy one cases of chronic virus hepatitis B (hepatitis B) with TCM clinical data were analyzed by information entropy method. RESULTS: It was found that hepatitis B with Yin deficiency of liver and kidney happened more often in summer than in other seasons. CONCLUSION: It is inferred that the difference of seasons may influence the variation of TCM syndromes.