The invention discloses a corn grain threshing and separating device and a combine harvester with the separating device. The corn grain threshing and separating device comprises a threshing roller which is provided with threshing teeth with ball-headed top ends, wherein a threshing concave plate is arranged below the threshing roller and is arranged on a mounting rack, and multiple columns of staggered elliptical holes are formed in the threshing concave plate; a stone collecting tank is arranged at one side, close to a corncob source, of the mounting rack, and a stone collecting tank cover plate is arranged above the stone collecting tank. Through the threshing teeth, grains are prevented from being crushed, and the threshing effect is enhanced; the threshing teeth are matched with the threshing concave plate, so that under the condition of guaranteeing low grain crushing rate, high threshing performance, screening performance and passing characteristic, the working strength, reliability and stability are improved through the mounting rack, and mounting and repair/maintenance are facilitated; the stone collecting tank is closed by the stone collecting tank cover plate, so that corncobs are prevented from falling into the stone collecting tank; meanwhile, through replacing a threshing and separating attachment, on the basis of realizing rice/wheat harvesting, the effect of harvesting corn crops is realized, and the use ratio of the harvester is increased.