Artemisia scoparia is a herbaceous plant of the composite family and a widely distributed species with a high degree of adaptability. The phenotypic plasticity of A. scoparia in different levels of relative soil humidity was addressed in this paper, which has important ecological significance for revealing survival adaptation strategies of A. scoparia in heterogeneous habitats. The results showed that plant height, stem diameter, root length, root weight, and biomass all showed an increasing trend with an increase in soil relative humidity; these factors exhibited strong plasticity across the soil water heterogeneous habitat, whereas the root/shoot ratio showed no change. The order of the biomass of different parts was:upper part < middle part < lower part, and the lower part was significantly heavier than the upper part (P < 0.05). The number and weight of the head inflorescence in the high soil relative humidity (> 40%) habitat were significantly greater than that in the lower soil relative humidity (< 30% and 30%-40%) habitats. The absolute input of reproductive organs (lg R) increased with the increase of individual size (lg V) and showed a significant positive correlation (P < 0.001). The reproductive threshold was between 1.868-2.006 g. With the increase of soil relative humidity, the proportion of reproductive allocation was significantly increased (P < 0.001). There were significant positive linear correlations between vegetative organs and reproductive organs, weight, number of the head inflorescences, and underground and aboveground biomass (P < 0.001). This indicated that there were positive trade-offs between each pair. However, the weight of a single head inflorescence did not change significantly with the increase of individual size or the number of head inflorescences (P > 0.05), and there were no significant differences in the different soil relative humidity habitats and for the different parts of the plant (P > 0.05). The phenotypic plasticity of A. scoparia in the heterogeneous environment of soil water is one of the important mechanisms for its survival and reproduction.