The invention belongs to the technical field of materials, and relates to a door plate core material and a preparation method thereof. The door plate core material comprises a sound absorption film (3), a support frame (2), an adhesive film (4), a sound-absorption and heat-preservation material (1), an adhesive film (4'), a support frame (2') and a sound absorption film (3') in sequence from top to bottom, wherein the adhesive films (4, 4') coat between the support frame (2, 2') and the sound-absorption and heat-preservation material (1); and all the adjacent layers are connected with each other after being pressurized. The sound insulation mechanism of the sound absorption film structures adopted by the door plate core material with flame retardance, sound insulation and heat preservation is film resonance sound insulation. On the resonant frequency, the sound energy is mostly absorbed due to the acute film vibration; as gaps of the support frames between the sound insulation films and the sound-absorption and heat-preservation material form air layers, the sound transmission is effectively reduced, and the advantages of flame retardance and heat preservation are achieved.