The invention discloses a crystallizer and a crystallization method. The crystallizer is provided with at least one fluid flow passage, wherein one end of the fluid flow passage is provided with a material inlet, the fluid flow passage is successively divided into a transportation segment, a mixing segment and a crystal growth segment along the flow direction of feed liquid, the transportation segment is used for transporting the feed liquid to the mixing segment, a side wall of one end, which is far away from the crystal growth segment, of the mixing segment is further provided with a coolingmedium inlet, the cooling medium inlet is used for sending a cooling medium into the mixing segment, the mixing segment is used for realizing mixing of the feed liquid and the cooling medium, coolingthe feed liquid and enabling the feed liquid to generate a super saturation degree and dissolve out crystal, the crystal growth segment is used for growing the crystal and obtaining suspension liquidcontaining solute particles; the other end of the fluid flow passage is further provided with a material outlet, and the material outlet is used for continuously discharging the suspension liquid outof the fluid flow passage. The crystallizer and the crystallization method can be used for rapidly generating a greater super saturation degree and relatively uniform super saturation degree distribution, thereby preparing a crystal particle product which is narrow in particle size distribution and small in mean particle size.