The inventio relates to a paper box forming device, which comprises a base plate, a shifting plate and elastic elements. A storage cavity is arranged on the base plate; the shifting plate is arrangedon a side wall of the storage cavity; the width of the shifting plate is smaller than the depth of the storage cavity; the shifting plate is arranged close to an upper surface of the base plate; at least one end of the shifting plate is fixedly connected with the elastic elements; and the elastic elements are at a compression state all the time and have a trend on pushing the shifting plate into the storage cavity. When the paper box forming device is used for pasting a paper packing box in an up-and-down direction, the shaping of a loosened box-shaped body at the lower part can be realized, aloosening trend of the loosened box-shaped body is prevented, and the pasting in the up-and-down direction is realized favorably.