Embodiments of this application relate to the field of battery cathode material technologies, and provide a nano-silicon composite material and a preparation method thereof, an electrode material, and a battery, to resolve large volume expansion of a cathode material of a battery and a serious side reaction with an electrolyte. The nano-silicon composite material includes a core, a first coating layer, and a second coating layer. The core includes a nano-silicon crystal. The first coating layer covers a surface of the core. The first coating layer is of a porous structure. A material of the first coating layer includes bisilicate and silicon oxide in a deoxidized state. The second coating layer covers a surface of the first coating layer. A material of the second coating layer includes silicon dioxide in a deoxidized state.