In this paper, the theoretical analysis proves that the relationship between radius r of jet and the axial distance z from the onset of whipping instability follows an allometric law in the form r ∝ z-1/4 whatever surface charge parameter a is. Polyvinylalcohol (PVA) was used to study the effect of surface charge on the variation of jet diameter with axial coordinate after the onset of whipping instability during electrospinning by adding LiCI. The experiment shows that the relationship between radius r of jet and the axial distance z from the onset of whipping instability also follows the law in the form r∝ z-1/4 whenthe content of LiCl is from 0.2 wt% to 4 wt%. That is, the law does not depend upon the content of salt, and the theoretical prediction agrees quite well with the experimental data.