In order to study the diffusion law of gun smoke after blasting in a single-headed roadway, combining the actual mining road as a test object, the change of the CO concentration in the gun smoke after blasting with time was measured, and the analysis of the measured data was obtained: When the CO concentration reached the peak, its concentration value showed an e-exponential decay trend, which was in line with the negative exponential decay change law, and quickly decreased below the allowable safe concentration; and the linear regression method was used to obtain that the CO concentration at different locations in the pedestrian roadway of the mine, when reduced to standard, the time calculation formula was got, which provided the basis and reference for the underground operators to return to the driving face again.