A threshing and separating device comprises a first threshing and separating mechanism, a second threshing and separating mechanism, and an intermediate feeding mechanism therebetween. The first threshing and separating mechanism comprises a first cylinder in a form of a toothed rod and a first concave in a form of a wire-grate, and a surface of the first concave facing the first cylinder is provided with no part protruding into a tip circle of threshing teeth of the first cylinder; the second threshing and separating mechanism comprises a second cylinder in a form of a toothed rod and a second concave in a form of a wire-grate, and a surface of the second concave facing the second cylinder is provided with no part protruding into a tip circle of threshing teeth of the second cylinder; the second cylinder comprises a forced feeding portion located at front end thereof and comprising a truncated cone and helical blades on the truncated cone; and a toothed-rod cylinder portion located behind the forced feeding portion and comprising a plurality of second rods parallel to the rotation axis of the second cylinder and uniformly arranged in a circumferential direction thereof, and each second rod is provided with a plurality of second threshing teeth.