A uniform air distribution device for an air chamber inlet of a grate-fired furnace comprises an inverted 'J'-shaped upper partition plate mounted on the upper portion of the air chamber inlet of the grate-fired furnace. The distance between the top end of the upper partition plate and a grate ranges from 10mm to 40mm, the length of an upper straight section of the upper partition plate ranges from 10mm to 20mm, the length of a lower straight section of the upper partition plate ranges from 25mm to 40mm, the total height H1 of the upper partition plate is equal to a+ (0.3-0.4) x, a 'balancing hole' 2 is arranged on a vertical portion of the upper partition plate, and the distance S1 between the upper partition plate and an air inlet of an air chamber is equal to (0.5-0.6)X(0.25-0.3) L, wherein the a refers to the distance between the grate and the upper portion of the air inlet, the x refers to the height of the air inlet, and the L refers to the length of the air chamber. By the aid of the uniform air distribution device, fine air distribution uniformity of the air chamber is ensured, resistance is controlled within a narrow range, and conditions are created for improving the operation efficiency of the grate-fired furnace, saving energy and reducing emission.