Root growth strategies are important to predict plant – soil interactions under nutrient-limited soil environments. A dominant species Stipa breviflora is found to develop cluster fragmentation in the arid and semi-arid areas of China, where water, nitrogen and phosphorus are the most important limiting factors to plant growth. Here, we aimed to assess how water, N, P additions and their interactions, and cluster fragmentation affect root growth traits in a greenhouse experiment to reveal the adaptation of S. breviflora under drought conditions. A standard Taguchi L8(27) arrays design was conducted with four factors such as nitrogen (N), phosphorus (P) and water (W) and cluster fragmentation (C) and three interactions (N × P, N × W and P × W). Each of four factors had two levels (N1 = 15 mg N / kg, N2 = 120 mg N / kg, P1 = 2 mg P2O5 / kg, P2 = 24 mg P2O5 / kg, W1 = 25 % ~ 30 % field moisture capacity of mixture (FMC), W2 = 75 % ~ 80 % FMC, C1 = individual with single ramet, C2= individual with three ramets).Water was the most important contributor to S. breviflora root system growth, while cluster fragmentation was the second contributor, followed by N and P in order. W2 and P2 both promoted root growth, whereas N2 significantly inhibited root growth. Moreover, under drought condition, N2 induced its roots developing an acquisition resource use strategy for escaping adverse environments compared to N1. While under sufficient P condition, W1 induced its roots developing an acquisition resource use strategy for acquiring more resource. And cluster fragmentation is beneficial to improving the adaptability of S. breviflora under low N condition.