The explosion characteristics and hazards caused by dispersion of the natural gas containing carbon dioxide are concerned about. In order to confirm the hazard zone determination during the dispersion of natural gas containing carbon dioxide, explosion characteristics and the accuracy evaluation for the numerical model, mechanism of the puff dispersion and dispersion issues caused by blowout were investigated by numerical simulation methods. A dispersion model of natural gas containing carbon dioxide was set up, and the dispersion evolvement was researched in detail, furthermore, the hazard zone concluding asphyxiation and explosion or flammability is defined. The numerical simulation results show that the flammability zone caused by the puff dispersion of the natural gas containing carbon dioxide takes on an irregular cirque distribution. Along-wind variation of flammability-zone dimension is larger than that for crosswind. For both cases of along-wind and crosswind, the distribution of variations of flammability zone with time presents the shape of parabola whose peak point is up. Besides, it does not matter to judge explosive zone based on time or on space, the affected area for flammability zone is way smaller than that for the asphyxia zone.