Soil electric field (E0) might have strong effects on rill erosion, and it is in turn largely affected by root growth. This study aimed to quantify the ability of roots to predict E0 and elucidate the effects of E0 on the mean weighted diameter of soil aggregates (MWD) and rill erodibility (Kr). Samples were collected from three typical areas in the Loess Plateau of China, and each area had two typical grasslands. Soil detachment rates were measured using a hydraulic flume under five discharges (0.1, 0.2, 0.3, 0.4, and 0.6 L s−1) on a slope of 15°. The results indicated that plant roots negatively contributed to E0. The mean E0 of grasslands (rooted soil) was lower by 3.27 times compared with that of fallow lands (root-free soil). With significant correlation (P < 0.05), root length density (RLD) and root surface area density (RSAD) were found to be suitable parameters for predicting E0, which decreased exponentially with RLD (R2 = 0.306) and RSAD (R2 = 0.381). In addition, E0 strongly affected MWD and Kr by influencing soil repulsive forces. E0 was negatively correlated to MWD (logarithmic function, R2 = 0.96), but positively correlated to Kr (linear function, R2 = 0.88). Our results provide new insight into the mechanism of rill erosion considering plant roots.