In order to improve the efficiency of gas drainage, clearing the reasonable gas drainage drilling hole sealing length, based on the factors affecting gas extraction from drilling hole sealing depth analysis, combined with the lane for the stress distribution state, drilling cuttings method was adopted to study gas drainage drilling hole sealing length. The result showed the gas extraction of drilling hole sealing depth for unloading area must be through the lane, only entering the higher stress area can play a good hole sealing effect. Drilling cuttings method measured Nanling Mine 4101 working face unloading zone and the peak stress position, reasonable hole depth of 8 ~ 10 m was settled, through the field application showed that gas extraction efficiency was improved by more than 25%.