The invention discloses a low-concentration gas flow powerless purification emission reduction which can be mounted on a mine exhaust fan diffuser or the tail end of a gas sucking and discharge tube, the flowing speed of a gas is reduced in modes of increasing the cross section of a channel, increasing the partial resistance, adjusting the size of an outlet and the like, and the gas with relatively low density is accumulated at the upper part of an air cylinder, enters an upper layer of speed reduction air cylinder through gas rising flowing tubes, is finally accumulated at a gas accumulation tube at an uppermost layer, and is output and utilized. When the concentration of the gas at the outlet of the speed reduction air cylinder cannot meet the emission standard, the concentration can be adjusted by reducing the size of the outlet of the air cylinder, lengthening the speed reduction air cylinder and increasing the number of gas rising flowing tubes, or another set of the device is connected for secondary purification; when the concentration of the gas in the gas accumulation tube cannot meet the use requirements, another set of the device for secondary purification can be also connected at the outlet till the use requirements are met. The device is simple in structure, energy-saving and environmental-friendly, easy to operate and low in cost, can be repeatedly used, and can be widely applied to low-concentration gas purification.