Understanding patterns of intraspecific trait variation can help us understand plant adaptability to environmental changes. To explore the underlying adaptation mechanisms of zonal plant species, we selected seven populations of Stipa krylovii, a dominant species in the Inner Mongolia Steppe of China, and evaluated the effects of phenotypic plasticity and genetic differentiation, the effects of climate variables on population trait differentiation, and traits coordinated patterns under each soil moisture treatment. We selected seeds from seven populations of S. krylovii in the Inner Mongolia Steppe, China, and carried out a soil moisture (2) × population origin (7) common garden experiment at Tianjin City, China, and measured ten plant traits of S. krylovii. General linear analyses were used to analyze how soil moisture and population origin affect each trait variation, Mantel tests were used to analyze population trait differentiation - geographic distance (or climatic difference) relationships, regression analyses were used to evaluate the trait-climatic variable relationships, and plant trait networks (PTNs) were used to evaluate the traits coordinated patterns. Both soil moisture and population origin showed significant effects on most of the traits. Aboveground biomass, root-shoot ratio, leaf width, specific leaf area, and leaf nitrogen (N) content were significantly correlated with climate variables under the control condition. Specific leaf area and leaf N content were significantly correlated with climate variables under drought conditions. By PTNs, the hub trait(s) was plant height under the control treatment and were aboveground biomass, root length, and specific leaf area under drought conditions. This study indicates that both phenotypic plasticity and genetic differentiation can significantly affect the adaptability of S. krylovii. In addition, soil moisture treatments show significant effects on trait-climate relationships and trait-coordinated patterns. These findings provide new insights into the adaptive mechanisms of zonal species in the semi-arid grassland region.