The invention provides a preparation method for a plane polymer composite material heating plate and a heating substrate thereof. The plane polymer composite material heating plate includes the heating substrate, electrodes, auxiliary electrodes and an insulating protective layer, wherein both sides of the heating substrate are respectively equipped with a positive and a negative electrode that are in parallel with each other, and the auxiliary electrodes are used for covering the heating substrate interval that is covered by the parallel positive and negative electrodes. The insulating protective layer is clad onto the outer layer of the heating substrate provided with the electrodes and the auxiliary electrodes. Wherein the heating substrate is composed of the following materials with acertain weight proportion: linear low-density polyethylene: 35 - 40 phr; metallocene polyethylene: 25 - 35 phr; conductive carbon black: 25 - 35 phr; antioxidant: 1 - 2 phr and composite nano-pole titanium dioxide:1 - 2 phr. And the heating substrate is smashed after mixing in a mixing roll and then is granulated by a single-screw extruder so that mixed master batches are made. After being mix-melted, dispersed and plasticized in a twin-screw extruder, the mixed master batches enter into a single-screw extruder and are extruded through the sheet forming mould, then the extruded mixed master batches are pressed by a three-roller plating press, into sheets that are finally cross-linked through electron beam irradiation of an electron accelerator.