Microbial prospecting of oil and gas (MPOG) technology was applied to the Gangxi area for determination of distribution of oil and gas. Combined with regional geological data, oil and gas well data and distribution of bio-limestone, the authors analyze the main controlling factors of the fault Qi-81 and reveal the law of oil-gas reservoirs. By comparing microbial anomaly values of the abnormal areas with zones of mature development and other anomaly areas, the authors find that the average value of the microbial anomalies of the area is lower than the other highly developed areas, resulting in a reasonable understanding of the hydrocarbon-bearing prospect of the block Qi-81.