The invention provides a preparation method for an all-solid-state battery. The method comprises the steps of S1, mixing lithium salt, additive and initiator to obtain mixed solution, wherein the additive is micromolecule monomer comprising unsaturated bond; and S2, carrying out in-situ polymerization and adhesion by the solution in a cathode layer, a solid electrolyte layer and an anode layer andamong the layers, thereby obtaining composite solid electrolyte, wherein a solid electrolyte layer comprises inorganic solid electrolyte and adhesive. Compared with the prior art, the method has theadvantages that through utilization of flowability of the micromolecule monomer additive comprising the unsaturated bond, solid particles are wetted sufficiently, ion transport channels are constructed through in-situ polymerization and solidification, electrode layers are adhered once, and a battery is moulded; the compatibility of the solid-solid interface in the all-solid-state battery can be effectively improved; and the preparation method is simple and fast, is compatible with the existing battery technology and is beneficial for large-scale preparation.