Abstract: The small aperture drilling blasting method has been very widely used for roadway excavation process. But in the roadway excavation blasting, explosives produced gas containing large amounts of toxic and harmful ingredients. Due to the relatively small roadway work space, poor ventilation conditions likely to cause excessive concentration of toxic gases, and pose a serious threat to health and safety of construction workers. This paper, we build model of migration law for fume after blasting in the pit which is based on previous research results and select real blasting tunnel for the study; experimental research methods for natural ventilation, the roadway changes of CO concentration was analyzed quantitatively; study results presented at different locations within the roadway CO concentrations up to standard time were calculated. A number of measures that people can safely go into the working face were proposed.