The utility model provides a rotary kiln for producing active lime. The rotary kiln comprises a gas producer, a gas flue, an inlet gas chamber, a rotary kiln body, an adapter, two stages of bearing derails, a big gear-pinion group, a motor, and a rotating machine connected with the motor through the big gear-pinion group, wherein a thermal insulating layer which is 3-40mm thick is formed on the inner wall of the rotary kiln body, the surfaces of fireproof bricks arranged on the inner cavity of the rotary kiln are in a projection shape; besides, the two stages of bearing derails are connected with the rotary kiln body, respectively. The thermal insulating layer structure and the projection structure on the surface of the inner cavity of the rotary kiln enable the thermal insulation performance of the rotary kiln to be superior to that of the conventional technique, and the projections on the surfaces of the fireproof bricks on the inner cavity of the kiln body cause material powder to be stirred thoroughly and evenly in the calcination process of the rotary kiln, therefore, the calcination effect is greatly optimized.