The invention discloses a gas extraction method and a gas extraction method. The gas extraction method comprises the steps of: making a support mould; arranging the top part of the support mould at the inner side of a filling wall in a gob side entry and placing the bottom end thereof on a base plate in the gob side entry to enable one side of the support mould, the base plate and a gap sidewall between the bottom end of the filling wall and the base plate to encircle a channel; plugging openings at two ends of the channel to form a sealed cavity; inserting an insertion pipe of a sealed container into the sealed cavity from the support mould; filling a filling material in the support mould to seal a gap between the insertion pipe and the support mould; sealing extracted mixed gas in the sealed container through a valve set on the insertion pipe; and measuring the quantity of flow of the mixed gas collected in the sealed container through a flow meter set on the insertion pipe. The gas subjected to pressure relief on the base plate is encircled in a sealed space without diffusing to airflow by adopting a way of encircling firstly and extracting secondly, and then the gas are gathered and extracted by utilizing the extraction system, so that gas rushing out of a gap can be extracted fully and efficiently.