The invention relates to a continuous graining, crystallizing and drying device for 1,3-polytrimethylene terephthalate (PTT). The continuous graining, crystallizing and drying device comprises a granulator, a crystallizing tower and a slice dryer which are connected with one another sequentially, wherein the granulator is provided with an inlet for inputting a melt continuously produced by PTT; the granulator is an underwater ball-milling granulator; water is filled in the underwater ball-milling granulator; granulating is performed in the underwater ball-milling granulator; produced granules and water enter the crystallizing tower together; in the crystallizing tower, the water temperature is controlled within a range of 75-85 DEG C, the retention time is controlled within a range of 1-5 minutes, and the flow speed of a water and slice mixture is controlled within a range of 1-3 meters per second. By adopting the continuous graining, crystallizing and drying device, the PTT granules have enough retention time to be fully subjected to underwater crystallization in the tower, and the glass transition temperature of the PTT granules is increased, therefore, the problem of sticky blocking of the PTT granules at high temperature can be solved effectively; and package and subsequent production work for the PTT granules are facilitated.