The invention relates to a gas mixing device including an air compressor having a gas inlet and a gas outlet; the gas mixing device also includes a first gas storage tank and a second gas storage tank for storing mixed gas; the first gas storage tank is connected with the gas inlet of the air compressor through a first pipeline; the second gas storage tank is connected with the gas inlet of the air compressor through a second pipeline; the first gas storage tank communicates with the gas outlet of the air compressor through a third pipeline; the second gas storage tank communicates with the gas outlet of the air compressor through a fourth pipeline; a first control valve, a second control valve, a third control valve and a fourth control valve for controlling on-off of the corresponding pipelines are correspondingly arranged on the first pipeline, the second pipeline, the third pipeline and the fourth pipeline; the air compressor pumps gas in the first gas storage tank into the second gas storage tank through the first pipeline and the fourth pipeline and pumps gas in the second gas storage tank into the first gas storage tank through the second pipeline and the third pipeline. The gases in the two gas storage tanks are circulated by the air compressor, the mixing speed of the mixed gas can be effectively accelerated, and the mixing requirement is achieved in a short time without long-term standing.