The invention discloses a preparation method of a sheet-shaped boron-doped porous silicon electrode material. The preparation method comprises the steps of (1) immersing boron-doped P-type silicon debris with an inorganic acid for 6-24 hours, and performing washing and drying to obtain boron-doped silicon powder; (2) uniformly mixing the boron-doped silicon powder and magnesium powder according toa mole ratio being 1:(1-2.5) to obtain a mixed material, and performing thermal processing on the mixed material under inert atmosphere to generate Mg2Si powder; (3) oxidizing the Mg2Si powder undera high temperature of 400-850 DEG C to obtain a reaction product, immersing the reaction product with the inorganic acid, cleaning and washing the reaction product with an HF solution, and obtaining the sheet-shaped boron-doped porous silicon electrode material after drying. The grain size of the prepared sheet-shaped boron-doped porous silicon electrode material is 0.2-5 micrometers, the specificarea is (10-100) m<2>/g, and the pore diameter is 20-70 nanometers. The sheet-shaped boron-doped porous silicon electrode material has favorable cycle stability and high specific capacity.