The invention discloses an irrigating device after corn planting, which comprises a water tank, a water holding cover, a power distribution box, an electric roll wheel, a water delivering disk, watering frames, a mounting ring, a chute, a water connecting pipe, a slide buckle pillar, a screwing bolt, a water cabin, a water receiving opening, a sealing plate, a connecting block, a water connectinghole, a water dividing disk, a motor, a rotary pouring disk, a sheathing disk, a watering rod, a driving gear, a sleeve block and a water outlet. The irrigating device has the beneficial effect that the device is high in automatic degree in use, free from labor operation, and saves time and force and guarantees the using convenience. People can change the extending length of the water connecting pipe by gliding the slide buckling pillar forwards and backwards on the chute of the mounting ring upon the watering demand of corn planting lands with different widths, thus the working positions of two watering frames can be changed, the watering position and the overall width of the whole device are changed; the device has more accurate soil watering position, the adaption universality is guaranteed; the device is convenient to operate, and every member is flexible in connection.