In order to study the substitution uniformity of carboxymethyl guar produced by split process，the internal cross-section element distribution of carboxymethyl guar split was analyzed by environmental scanning electron microscopy spectroscopy（ESEM-EDS），and the degrees of substitutions（DS）of different layers of carboxymethyl guar split were determined by 1H-NMR.The results showed that alkalizer NaOH diffused uniformly through the guar split，and the concentration of NaOH had no effect on its diffusion behavior. The etherifying agent sodium chloroacetate was unable to diffuse uniformly due to a large molecular. The content of sodium chloroacetate inside the split was lower than that of outside the split. The DS of the carboxymethyl guar split decreased from 0.291 for the outer layer to 0.197 for the inner layer，which revealed that the split process gave a heterogeneous product.