The present invention relates to a method for analyzing the length of sulfur crosslinking bonds in a vulcanized rubber using NMR spectrum. In some embodiments, the method comprises obtaining, independently, a carbon-13 nuclear magnetic resonance (13C NMR) spectrum of a standard substance, wherein the standard substance containing carbon atoms, and a 13C NMR spectrum of the vulcanized rubber, wherein the 13C NMR spectrum of the standard substance and the 13C NMR spectrum of the vulcanized rubber are obtained under the same conditions; obtaining, independently, free induction decay (FID) amplification values of characteristic peaks in the 13C NMR spectrum of the standard substance, and FID amplification values of characteristic peaks in the 13C NMR spectrum of the vulcanized rubber; and measuring the length of sulfur crosslinking bonds in the vulcanized rubber.