The invention discloses a tube-shell type ultrashort evaporator, comprising a shell in which two groups of U-shaped tube are disposed, wherein, the first group of U-shaped tubes are disposed in middle of the second group of U-shaped tubes, and each group is composed of a plurality of U-shaped tubes. A barrier is disposed between the two openings of the second group of U-shaped tubes, and a clapboard is arranged at the lower part of the two groups of U-shaped tubes. And a clapboard is arranged at the upper part of the two groups of U-shaped tubes, wherein, concavo-convex bodies are arranged onthe clapboards. Easy transportation is achieved due to adopt the two-circuit U-shaped tube, and the length of whole body is less than 2 meters. The gas phase and liquid phase can be rotated and fullymixed due to the clapboards with concavo-convex bodies which is arranged at the upper part of the two groups of U-shaped tubes, so that the cooling medium can be completely evaporated in an ultrashort tube-shell.