The invention relates to preparation of a sol, and aims to provide a preparation method of an organic-inorganic composite sol for metal aluminum sheet surface corrosion prevention. The method comprises the following steps: adding tetramethyl orthosilicate or ethyl orthosilicate into a saturated alcohol solvent of ammonia gas, adding water, reacting, heating under reflux to remove ammonia, and carrying out rotary evaporation to obtain a nano silicon dioxide sol; adding the nano silicon dioxide sol into a Al(OH)3 sol, and aging; adding a catalyst while stirring and keeping the pH value at 1-5, adding an acetylacetonate chelator, and continuing stirring; and dropwisely adding an organosiloxane-titanate mixture, and reacting to obtain the sol. The method greatly increases the adhesive force between the coating and metal aluminum sheet by 1-3 levels on the basis of the traditional silicon coating. The high-hardness Al(OH)3 is coated on the nano silicon dioxide particles to further enhance the coating hardness by 2H or so on the basis of the traditional silicon coating, and the corrosion resistance in a neutral salt fog resistance experiment is enhanced by 2-3 times.