Plant roots significantly affect soil erosion, while few works have pursued why root-penetrated soil obtained higher soil erosion resistance as compared with plain soil. For the purpose to investigate the relative contribution of root physical enlacing (root net-link and root-soil bond functions) and root biochemistrical exudates to soil erosion resistance. This study selected Purple alfalfa root- and designed root-penetrated Loess soil as study object, and subjected to flow scouring. The results showed that roots could significantly ameliorate soil properties, especially for soil enzymes. Root physical enlacing is the main reason, accounting for 77.7–82.0% of the root total effect in strengthening soil erosion resistance. And of this total, the relative contribution ratio of net-link and soil-root bond functions to soil erosion resistance was 0.71:0.29, averagely. Root surface area density could effectively reflect root physical enlacing effect. This kind of study may provide theoretical explanations for the root reinforcement in the flow-induced erosion regions. •Root physical enlacing contributes 77.7–82.0% of root effect to erosion resistance.•Contributing ratio of net-link:soil-root bond to erosion resistance is 0.71:0.29.•Root surface area density could effectively reflect root physical enlacing effect.