The present application provides a preparation method for a solid electrolyte, including: acquiring an initial reaction mixture including a lithium precursor, a central atom ligand and an organic solvent; acquiring a modified solution including a borate ester and the organic solvent; mixing the initial reaction mixture and the modified solution, and drying to acquire an initial product; performing a grinding, cold press and heat treatment to the initial product to obtain the solid electrolyte. In the preparation method provided by the present application, a B and O co-doped sulphide solid electrolyte can be obtained by modifying the sulphide solid electrolyte with the borate ester as a doping raw material. The ionic conductivity of the prepared sulphide solid electrolyte is significantly improved, which is also conducive to improvement of energy density of the all-solid-state batteries.