The basic principle of SOFC is described and a mathematical model for tubular SOFC is developed by proceeding from four conservation laws. The differential equations are calculated using the iterative method， and function image between output peak areas and contents of six kinds of combustible gas， namely， H2 ， CO， CH4 ， C2 H2 ， C2 H4and C2 H6 . The result shows that the curve is monotonic and almost linear in fixed scope. Combined with modern chromatography technology， an accurate on-line dissolved gas analysis（DGA） detection machine has successfully been developed. The operating results show that this technology can meet the need of DGA online detection and has such advantages as excellent linearity， high precision， convenience， cleanliness and auto-detection.