The invention discloses a method for extracting silicon from serpentine magnesium-extracting residues and preparing nano-mesoporous silica beads. The method comprises the following steps: preparing raw materials by adopting acid leaching; performing alkali melting, adding into a water bath and an oil bath, drying, calcining, extracting the silicon and preparing the nano-mesoporous silica beads. The process flow is simple, the magnesium-extracting residues are fully utilized to separate the silicon, resources are saved, and the pollution problem of the magnesium-extracting residues on the environment is solved. Moreover, the prepared nano-mesoporous silica beads are regular in morphology and large in specific surface area, have excellent dispersion properties, can be applied to dispersing agents, molecular sieves and catalyst carriers and have wide application range.