Agricultural breeding device convenient for water body replacement

The agricultural breeding device comprises a frame, a box, a seedling bed, an automatic water control assembly and a convenient drainage assembly, a first water tank is fixedly connected to the upper portion of the frame, a first water pipe is fixedly connected to the left side of the first water tank, the box is arranged at one end of the first water pipe, and the seedling bed is arranged above the box; an automatic water control assembly is installed on the upper left portion of the box, a convenient drainage assembly is installed on the lower left portion of the box, a second water tank is arranged below the frame, an electromagnet is powered on to attract a magnet to ascend, a long rod and a lower plug block are pulled to move upwards, and therefore a lower horn opening is formed, water is conveniently drained, and meanwhile when water is drained, a floater is automatically jacked up to avoid water supply above the floater; and after the water is completely discharged, the electromagnet is powered off, th