Abstract: Modified expandable graphite was prepared and used in the synthesis of benzaldehyde glycol acetal under microwave irradiation. The factors were investigated through orthogonal experiment. The optimum conditions were as follows: molar ratio of benzyladehyde to glycol 1:2.5, mass ratio of the catalyst to the total reactants 2.04%, microwave irradiation power 300W, irradiation time 20.0 min, and the amount of cyclohexane was 6mL, the yield of acetal reached 87.6%; and the activity of the catalyst remains basically unchanged after used 4 times. The catalyst was studied by SEM and XRD, which showed that interlayer compound was instituted by sulfuric acid molecules inserting the graphite’s layers.