The invention relates to a dryer for drying materials by gas. The dryer comprises a sealed case, wherein at least one feeding hopper is arranged on one end of the sealed case while at least one discharge hopper is arranged on the other end of the sealed case; the sealed case is internally provided with a material transfer mechanism at least part of which moves along a direction from the feeding hopper to the discharge hopper of the sealed case; a gas inlet and a gas pumping hole are also formed in the sealed case; and gas for drying and exchanging heat flows into the sealed case from the air inlet, moves in a direction opposite to the material transfer mechanism to realize countercurrent-flow heat exchange, then flows outside from the gas pumping hole. The dryer provided by the invention can select low-calorific-value and low-pressure gas, such as low-pressure steam and low-temperature smoke, as a heat source to dry the materials, thereby fully utilizing residual gas and tail gas, and improving the utilization rate of energy sources. In addition, the dryer can be used for prolonging material drying time and improving the heat exchange efficiency between the materials and the gas; and the number of material drying plates can be reduced or increased according to the quantity of materials to be dried, thereby improving the drying efficiency.