A moving granular bed includes a filter granule channel, an inlet unit of gas, an outlet unit of gas, a first detecting unit and a feedback control unit. The inlet unit of gas is disposed at one side of the filter granule channel, and the dirty gas is fed into the filter granule channel through the inlet unit of gas. The inlet unit of gas has a first flow-guiding plate. The outlet unit of gas is disposed at the other side of the filter granule channel. The first detecting unit detects the gas velocity at the inlet unit of gas site. The feedback control unit is electrically connected with the first detecting unit, and controls the angle of the first flow-guiding plate and flow rate of filter granules according to a detecting result of the first detecting unit. A gas guiding system used in the moving granular bed is also disclosed. The moving granular bed and gas guiding system can make the dirty gas have different velocity or distribution while passing through the filter granule channel so as to improve the usage of the filter granules.