The invention discloses a method for detecting internal resistance of a sodium-sulfur battery, comprising the following steps: selecting a plurality of remaining capacity points in a remaining capacity range of 0-100%, and selecting a plurality of battery temperature points in a temperature range of 280-360 DEG C; fitting a curvilinear equation of internal resistances in the sodium-sulfur battery, corresponding to the remaining capacity points, relative to battery temperature changes; calculating theoretical values of the internal resistances in the sodium-sulfur battery according to the curvilinear equation of the battery internal resistances in the sodium-sulfur battery relative to the battery temperature changes, calculating differences with measurements, correcting the curvilinear equation of the internal resistances in the sodium-sulfur battery relative to the battery temperature changes to obtain a standard curvilinear equation of the internal resistances in the sodium-sulfur battery relative to the battery temperature changes. The method has the advantages that according to battery internal resistances, temperature differences are compensated in the process of evaluating electrical performance of the sodium-sulfur battery and determining health state process of the sodium-sulfur battery, and the electrical performance of the sodium-sulfur battery can be evaluated and the health state of the sodium-sulfur battery can be determined more accurately.