Abstract: Combined with cases of difficult diseases， professor Wang Canhui's experiences on treating difficult diseases with replenishing qi， clearing heat and activating blood are introduced. For pathogenesis of difficult diseases， professor Wang considers that qi deficiency is the main pathological basis， and heat stagnation and blood stasis are the important pathogenic factors. The three factors are reciprocal causation and their pathogenic changes influencing each other lead to prolonged of disease course.