The invention relates to a method for preparing a lithium battery silicon carbon anode material by utilizing magnesiothermic reduction. The method comprises the following steps: preparing a mixed solution of sodium silicate, glucose and sodium chloride; heating and drying to obtain a brown caramel-shaped precursor; heating the precursor to 650 DEG C for calcining in the atmosphere of Ar to obtain a sodium silicate/carbon precursor; adding HCl into the sodium silicate/carbon precursor to prepare a mixed solution by utilizing a principle of preparing weak acid by strong acid; subsequently, drying the mixed solution in a drying oven at 170 DEG C; washing a sample with water to obtain a silicon dioxide/porous carbon composite material; uniformly mixing the silicon dioxide/porous carbon composite material, magnesium powder and sodium chloride; calcining at 700 DEG C, and performing acid treatment, water washing and drying to obtain a silicon carbon composite material. According to the method, a carbon/silicon dioxide composite material can be directly reduced and the silicon carbon composite material is successfully prepared.