Soil salinization can occur in many regions of the world. Soil sodicity affects rainfall-runoff relationships and related erosion processes considerably. We investigated sodicity effects on infiltration, runoff and erosion processes on sodic soil slopes for two soils from China under simulated rainfall. Five sodicity levels were established in a silt loam and a silty clay with clay contents of 8.5% and 46.0%, respectively. The soils, packed in 50 cm × 30 cm × 15 cm flumes at two slope gradients (22° and 35°), were exposed to 60 min of simulated rainfall (deionized water) at a constant intensity of 125 mm h−1. Results showed that, for both soils, increasing soil sodicity had some significant effects on hydrological processes, reducing the infiltration coefficient (pr = −0.69, P < 0.01) and the quasi-steady final infiltration rate (pr = −0.80, P < 0.01), and increasing the mean sediment loss (pr = 0.39, P < 0.05); however, it did not significantly affect the cumulative rainfall to ponding (P > 0.05). Moreover, increasing sodicity significantly increased the Reynolds number and the stream power (pr = 0.78 and 0.66, P < 0.01, respectively) of the runoff, decreased Manning roughness and Darcy-Weisbach coefficient (pr = −0.52 and −0.52, P < 0.05, respectively), but did not significantly affect the mean flow velocity, mean flow depth, Froude number and hydraulic shear stress. Stream power was shown to be the most sensitive hydraulic variable affecting sediment loss for both soils. Furthermore, as sodicity increased, the values of critical stream power decreased for both the silt loam (R2 = 0.29, P < 0.05) and the silty clay (R2 = 0.49, P < 0.05). The findings of this study were applied to a real situation and identified some negative effects that can occur with increasing sodicity levels. This emphasized the importance of addressing the influences of soil sodicity in particularly high risk situations and when predicting soil and water losses.