To explore the occurrence mechanism,clinical characteristics,differentiation principle of suspected complex syndrome from clinical thinking pattern.The emergence of suspected complex syndrome is closely related to the occurrence,development and turnover of diseases and their pathogenic factors and influential factors.Suspected complex syndrome is featured by incomplete symptom,multiphase similarity and impurity of single syndrome.The symptoms share causal relationship,true and false relationship or combination relationship.In clinic differentiation,basic principle of individuality has to be considered,then analyzed by critical thinking from a multi-aspect,multi-level,multi-relation angle so as to differentiate the major syndrome.Moreover,the specificity and non-specificity of symptoms,typical manifestations and atypical manifestations,unary and multiple differentiation of symptoms should be dealt with caution.