The utility model discloses a hot-air furnace device with V-shaped slits and a trapezoidal fire grate. The hot-air furnace device comprises a furnace body, a furnace top, a furnace door, an ash door, a combustion-supporting blower pipe, a lining and the fire grate. The furnace top is arranged on the top of the furnace body, and wavy fins are welded on the furnace top. The hot-air furnace device has the advantages that the cold air and flue gas heat exchange areas can be enlarged, and accordingly the hot-air furnace device is favorable for exchanging heat between cold air and flue gas; the V-shaped slits are arranged on the side walls of the trapezoidal fire grate, the trapezoidal fire grate which is of a trapezoidal structure is favorable for burning coal in the middle of the hot-air furnace device in a concentrated manner, the V-shaped slits are used as secondary air inlets, air which flows into a burning area from the V-shaped slits not only can provide oxygen for reburning volatile components generated when the coal is pyrolyzed, but also can be used as burnout air for providing oxygen for burning out the coal, accordingly, the coal can be burned sufficiently, and the coal burning efficiency can be improved; the coal is mainly burned at a middle rear position of the fire grate in the concentrated manner, furnace bars which are close to the furnace door are flat plates, accordingly, a large quantity of air can flow into a middle rear hearth, and the hot-air furnace device is favorable for completely burning fuel.