The invention provides a method for preparing solar grade silicon from silica serving as a raw material. In the method, the silica serves as the raw material, and CaCl2 is taken as a molten salt electrolyte; and the method comprises the following steps of: reducing the silica at the temperature of between 600 and 1,000 DEG C by using the molten salt electrolyte to directly electrolytically reduce silicon in the silica into elementary silicon; adding a compound into the elementary silicon according to a mass ratio of 1:3-9, and introducing protective gas at the temperature of between 600 and 1,200 DEG C for crystallization; putting the crystalized silicon into hydrochloric acid liquid with the concentration of between 1 and 5 mol/L according to a solid-liquid mass ratio of 1:1-8, and performing acid leaching for 2 to 48 hours; washing by using water for 2 to 5 times, and drying at the temperature of between 40 and 150 DEG C; melting the dried silicon at the temperature of between 1,450 and 1,650 DEG C, and performing vacuum evaporation under the vacuum condition at the temperature of between 1,600 and 1,650 DEG C and under the pressure of between 1*10<-2> and 1*10<10> Pa; and condensing the evaporated melt silicon at a condensation speed of between 0.1 and 5 mm/h to prepare the solar grade silicon. By reducing to remove impurities such as oxygen, phosphorus, aluminum, calcium, titanium and the like, and through high temperature crystallization and acid leaching for removing boron, the product has the purity of over 99.99991 percent, and the method has the advantages of short production flow, low cost and light environment pollution.