The invention discloses a capacity attenuation judgment method of sodium-sulfur energy storage equipment. The capacity attenuation judgment method comprises the following steps of 1, discharging, in which constant-current discharging is performed on the running sodium-sulfur energy storage equipment with a rated discharge current, and the sodium-sulfur energy storage equipment is discharged to a discharge cutoff voltage and stands for 1-24 hours; and charging, in which constant-current charging is performed on the sodium-sulfur energy storage equipment with a rated charge current, the sodium-sulfur energy storage equipment is charged to a charge cutoff voltage and stands for 1-24 hours, and the charging capacitor Qc is metered; and 2, discharging, in which constant-current discharging is performed on the sodium-sulfur energy storage equipment with the rated discharge current, the sodium-sulfur energy storage equipment is discharged to the discharge cutoff voltage, and the charging capacitor Qd is metered; and calculating coulombic efficiency, in which the calculation formula of the coulombic efficiency Eta is as follows: Eta=Qd/Qc*100%; and judging attenuation, in which capacity attenuation occurring in the sodium-sulfur energy storage equipment is judged when the coulombic efficiency of the sodium-sulfur energy storage equipment is larger than or equal to 101% or smaller than or equal to 99%. The capacity attenuation judgment method has the technical effects of high sensitivity, good enforceability and the like, and is simple to operate.