The invention belongs to the field of food additives, and in particular relates to a cake powder modifier and a preparation method thereof. The cake powder modifier comprises the following components in parts by weight: a plant extract, calcium stearate lactate, sodium stearyl lactate, compound enzyme, resistant starch, propylene glycol alginate, trehalose and an anti-caking agent. By adopting the cake powder modifier provided by the invention, on one hand, the quality of cakes can be effectively improved, on the other hand, the use amount of an emulsifier can be greatly reduced, and due to addition of the resistant starch and the propylene glycol alginate, the quality of cake powder is relatively well stabilized, and cakes made of the improved cake powder can be uniform and accordant in color, free of spot, free of sinking or swelling in appearance, uniform in thickness, soft in surface, fine and dense in internal texture, uniform in air pore, free of pimple and soft and tasty. The invention further provides a method for extracting medicinal materials by using normal-voltage positive and negative current together with high-frequency high-voltage current. The method has the advantages of low temperature extraction, low energy consumption, high extraction yield and short time, and has wide application prospects.