The present invention belongs to the field of sodium ion batteries. Disclosed is a preparation method for a sodium-based modified phenolic resin. The method comprises: a phenolic compound and an aldehyde compound undergoing a condensation reaction under the action of an alkaline catalyst to obtain an amino phenolic resin; carrying out a neutralization reaction by using 5-amino-1,2,3-benzenetricarboxylic acid and a sodium hydroxide solution; and adding an organic solvent, the amino phenolic resin, triethylamine and glycidaldehyde diethyl acetal to carry out an addition reaction, so as to obtain the sodium-based modified phenolic resin. Also provided in the present invention is a preparation method for a sodium-based modified phenolic resin hard carbon negative electrode, comprising: carbonizing the sodium-based modified phenolic resin in an inert atmosphere, grinding same and screening same to obtain an active substance; uniformly mixing the active substance, a conductive agent and a binder, coating a copper foil with same, drying same and rolling same to obtain a sodium ion battery negative electrode sheet. The methods effectively improve the capacity and the initial coulombic efficiency of the hard carbon negative electrode, thereby effectively improving the electrochemical properties of sodium ion batteries.