An evaporative crystallizer specially used for an MVR system for manganese sulfate and zinc sulfate materials is disclosed. The evaporative crystallizer includes a hollow tank body inside which an axial flow circulating heat exchanger including a steam heater is disposed. The steam heater is provided with heat exchange pipes inside, and is provided with a flow guide barrel in the middle. A stirrerallowing a heated material to fluidly move downward, towards the outside of the steam heater and then move upward is disposed in the flow guide barrel. The top of the tank body is provided with a secondary steam outlet. A liquid feeding pipe is disposed at one side or a plurality of sides of the tank body, and a material discharging pipe is disposed at the bottom of the tank body. The integratedevaporative crystallizer overcomes a problem that evaporative crystallization devices for manganese sulfate and zinc sulfate materials at present have disadvantages including pipe blockage of heat exchangers and fine crystal particles, facilitates ecological environment protection, and reduces the cost of production energy consumption for manganese sulfate and zinc sulfate materials. An evaporative crystallization method achieving no pipe blockage and allowing crystals to grow by utilizing the evaporative crystallizer is further disclosed by the invention.