The invention discloses a method for preparing lithium hydroxide monohydrate by extracting lithium from spodumene. The method includes steps of transformation roasting, cooling, ball milling, acidification roasting, pulping, neutralizing, separation washing, purifying, blending for transformation, freezing for sodium precipitation, deep decontaminating, evaporative crystallization, centrifugal separation, drip washing and drying. By means of a DTB (draft tube baffle) type crystallizer, an FC (forced circulation) crystallizer or an OSLO crystallizer, continuous cooling crystallization and evaporative crystallization are realized, equipment yield is increased by more than 50%, and equipment utilization rate is increased. Therefore, the method is simple and practical in process, high in equipment yield, low in production cost, high in resource utilization rate, low in energy loss and low in three wastes (waste gas, waste water and waste residues).