Although many studies have studied the effects of single environmental factor (temperature, precipitation, CO₂ etc.) on plants, the interactive effects of changing precipitation and temperature on plants, especially of multiple precipitation and temperature regimes have drawn few attention to date. Stipa breviflora, which is one of the dominant species of desert steppe in the arid region, would be highly sensitive to changes of temperature and precipitation. Our objectives of this study are to determine the interactive effects of changing precipitation and elevated temperatures on biomass and its allocation of S. breviflora, and to discover its sensitive organs, in order to provide a reference for the biomass change of S. breviflora in the future climate scenarios and the adaptability of desert steppe to future climate change. In this paper, five artificial control chambers were used to simulate the elevated temperatures (control, T1.5, T2.0, T4.0, T6.0) and changing precipitation (W-30%, W-15%, control W0, W+15% and W+30%) (based on the average monthly temperature and precipitation of 6-8 months during 1978-2007 in Siziwangqi county, Inner Mongolia). There are six replicates for every temperature and precipitation treatment. The seeds were sowed and well watered before control experiment in greenhouse. Then, 150 pots of plants (four plants per pot) with consistent growing vigor were randomly selected and placed into five artificial control chambers as different treatments. Temperature treatments were controlled by artificial control chambers with different daytime and nighttime temperatures, each precipitation treatment was converted to irrigation amounts of every month and then divided into 10 times to water. The biomasses of S. breviflora were measured based on leaves, stems and roots after 3 months. The results showed that the interactive effects of elevated temperature and changing precipitation on biomass and its allocation of S. breviflora were significant. Total biomass, leaf biomass and root biomass increased due to warming, stem biomass and root shoot ratio (R/S) decreased with the increase of temperature when warming was more than 1.5 ℃ and 4 ℃. With the warming of 6 ℃ and decreased precipitation of 30%, total, leaf and root biomasses decreased significantly, but stem biomass and R/S were not affected significantly. With warming and increasing precipitation, total, root and leaf biomasses of S. breviflora increased, stem biomass increased only when warming was less than 2 ℃, so warming and increased precipitation within an appropriate range might promote biomass accumulation. Under interactive effects of warming and changing precipitation, the sensitivity of organ biomass allocation of S. breviflora was ranged as shoot mass ratio (SMR)> leaf mass ratio (LMR)> root mass ratio (RMR), the stem was the most sensitive organ. S. breviflora would adapt to the future climate change by adjusting the biomass allocation into different organs based on its sensitivity. There was difference between the interactive effects of temperature and precipitation and its single effect, therefore we should consider the scene of interactive effects of temperature and precipitation in predicting the adaption of desert grassland plants.