[Objective] Jag S is a kind of new macromolecule polymers which can regulate water and soil loss. Studying Jag's chemical regulation effect on the rainfall infiltration can provide the scientific basis for the control of soil and water loss on loess slope.[Methods] A simulated rainfall experiment was conducted to study the regulating effect of Jag S on infiltration of loess slope.[Results] (1) Variation trend of the infiltration rate of the slope with the spreading of Jag S was similar to bare soil. It rapidly decreased at first and then stabilized with the increase of the rainfall duration.(2) Compared to the bare soil, the soil with spreading Jag S had greater reduction of infiltration rate, less initial runoff time and less time for the infiltration rate to be stable, and the infiltration rate in the soil with dry spreading Jag S was lower than bare soil, but its stable infiltration rate was higher than bare soil.(3) Infiltration amount of the soil with spreading Jag S was significantly higher than bare soil. With different doses, the infiltration capacity decreased with slope increase, and increased with the increasing rainfall intensity.[Conclusion] The dry spreading Jag S increased the infiltration capacity, the regulating effect of different doses was 1 g/m² >3 g/m² >5 g/m².