Abstract: According to the carbon dioxide injected at early stage of coal bed methane exploration could cause strata pressure increased at spread parts,thus the rado n air vertical upward migration was blocked and a feasibility study was conducted on carbon dioxide injection in the seam affected to ground surface radon density in the re lated region and active carbon radon detection method applied to monitor and measure the carbon dioxide distribution features. After annual monitoring and measuring wer e conducted on the radon density variation in the test block,the fractal dimension analysis method of variance function was applied to process the original data collected. T he study results showed that carbon dioxide injection in the seam could make the radon distribution in relevant ground surface of carbon dioxide related region to be in bal ance and the radon density variation in different directions would be different obviously. The active carbon radon detection method could effectively monitor and measure th e carbon dioxide distribution features in the seam to replace methane.