[Objective] The impacts of Achnatherum splendens patches on rainfall partitioning and surface runoff were studied to provide a basis for revealing the formation of vegetation patches and the mechanism of water regulation recognition.[Methods] The deep-rooted grass of A. splendens was used in the Qinghai Lake watershed as an indicator plant to calculate the water compensation ratio of A. splendens patches in the horizontal direction by observing the redistribution of rainfall and surface runoff in the crown of A. splendens patches.[Results] ① The throughfall of the A. splendens patch accounted for 70.58% of the total rainfall and was mainly affected by rainfall, rain intensity, and duration. This was similar to most shrubs in arid ecosystems. ② The mean runoff coefficient of the A. splendens patch was 0.45%±0.33%. This was significantly lower than that of the matrix (2.08%±1.46%) and increased with rainfall. ③ The water compensation of the A. splendens patch accounted for 1.13%±1.34% of total rainfall, and it increased with rainfall and rain intensity. The highest value of the proportion of water compensation was 4.94%.[Conclusion] The A. splendens patch can be recharged by the runoff from the matrix in the ecosystem scale, which is the water regulation mechanism of drought adaptation for patchy vegetation in arid regions.