Disclosed is a limestone slurry and lime milk preparing device for hydrometallurgy of laterite nickel ore, which relates to the technical field of limestone slurry and lime milk preparation and comprises a limestone slurry preparation assembly and a lime milk preparation assembly. The limestone slurry preparation assembly comprises a first feeding machine, a grinding mill, a mixing machine, a first transfer pump, and a first buffer tank, connected sequentially. When the weight of the limestone slurry in the first buffer tank is not within a first preset range, the first feeding machine, grinding mill, mixing machine, and first transfer pump can adjust their respective operating speeds. The lime milk preparation assembly comprises a lime kiln, a second feeding machine, a nitrifying machine, a third transfer pump, and a second buffer tank, connected sequentially. When the weight of the lime milk in the second buffer tank is not within a second preset range, the lime kiln, second feeding machine, nitrifying machine, and third transfer pump can adjust their respective operating speeds. The entire production line can respond in coordination, with overall automated adjustment of production efficiency and a high level of intelligence.