Abstract：This study analyzes the application of circuit and qi theory recorded in Pu Fu Zhou Yi An（ PU Fuzhou's Medical Case Records） and Pu Fu Zhou Yi Liao Jing Yan （PU Fuzhou's Clinical Experience）， focusing on his approach to treating external diseases. Key aspects examined include his principle of one must know in advance the condition of the qi of the year before treating disease，identifying six-qi diseases，theory of root （wind，cold，heat， dampness，dryness，and fire），branch（ taiyin，shaoyin，jueyin，taiyang，yangming，and shaoyang），and zhongqi （the qi that can be seen in one of the six qi，which transforms to the opposite direction when changing to a certain extent）， latent qi diseases， while emphasizing individual differences and integrating circuit and qi theory with syndrome differentiation and treatment. This study demonstrates that PU Fuzhou's clinical application of circuit and qi theory follows a well-defined logical framework and practical pathway： First， establishing the "one must know in advance the condition of the qi of the year before treating disease" principle， defining external diseases as "six-qi diseases，" delineating the corresponding temporal stages and clinical manifestations from initial qi to terminal qi，and expounding the "six-qi as root， six meridians as branch" theory. Second， emphasizing latent qi diseases including latent summerheat and latent cold transforming into dryness， considering latent qi as fundamental etiology requiring "treatment focusing on the root cause and expelling pathogens." Third， demonstrating flexible treatment adaptations based on yearly circuit， sitian-zaiquan yearly circuit qi through three epidemic cases： the outbreak of epidemic encephalitis B in Shijiazhuang in 1954，the outbreak of epidemic encephalitis B in Beijing in 1956，and the outbreak of measles in Chengdu in 1945. Fourth，highlighting the need to integrate circuit and qi theory with individual differences including constitution and living habits. Fifth，deeply incorporating circuit and qi theory into syndrome differentiation and treatment， embodying the holistic concept of "harmony between human and nature， " while proposing clinical principles of "know what a healthy condition looks like，and look into the range of healthy conditions" and "treatment focusing on the root cause."