Abstract: Based on the gas radial flow theory, flow rate changes with time of negative exponential attenuation law. Through formula derivation and examples of analysis, the paper finally determined that in the conditions of determinating initial time of t₀, selection of different time and the different flow metering mode had no impact on the calculation of the attenuation coefficient, but borehole gas initial flow q₀ soloved by different calculations is not the same, which is conducive to the measurement and analysis application of the attenuation coefficient in the actual process.