The invention discloses a method for curing in-situ soil in situ and a stirring device. The stirring device comprises a stirring arm. The two sides of the bottom of the stirring arm are provided with two inwards-inclining inclined faces. At least one mixing roller is arranged on each inclined face and driven by a drive device to rotate. The mixing rollers are in a topped cone shape. The method includes the steps of draining and leveling the surface of the in-situ soil, dividing in-situ soil blocks, stirring the preprocessed in-situ soil through the stirring device, and conducting leveling and prepressing. The method is constructed in situ, and therefore the problem that in the prior art, manufacturing cost is increased due to the transportation of dredger fill and stabilized soil is solved; the stirring device is wide in processing range and can process soft soil of different water contents.