Abstract: Before unsealing fire zone, it was very critical to judge fire zone burning state accurately, which largely determined the success rate and safety of unsealing fire zone. Though increasing oxygen concentration of fire zone by drilling holes, it used beam tube monitoring system which was from surface boreholes to the original fire point to monitor the change of gas concentration, observe the fire generated gas in fire zone, such as CO, C₂H₄, C₂H₂ and so on, they did not have upward trend in concentration, so it was sure that the fire in fire zone was really out indeed, which ensured unsealing fire zone successfully at one time.