Abstract: The article presents the difficulties of drilling gas effective extracting radius inspection process, analyzes the grey-scale relations of measuring parameters using the method of stress index. Establishes a gray prediction model and compares the data with the measured data, presents the grey forecasting theory of the effective drainage radius of borehole gas. The conclusion is to predict the maximum value in the twenty-fifth day to the pressure gauge is below 56%, and with the total observation time, prediction of the gauge has continued to decline, and measured twenty-third days of data is only 2 days.. The research results show that the grey forecasting model is proposed, in order to overcome the difficulties in the process of extracting the effective drainage radius of effective drainage radius of drilling gas, a reliable theoretical basis and data comparison are provided.