Plant root respiration is a primary component of soil respiration. In-depth research on plant root respiration is of great importance in understanding the budget and balance of ecosystem carbon storage. The present study used ¹³C pulse-labeling technology to evaluate changes in excised root respiration rates and root δ¹³C isotopic values of Bothriochloa ischaemum after different excision times (0 h,6 h,24 h,48 h,216 h,and 360 h after labeling) and analyzed the relationships between plant root parameters and excised root respiration. The results showed that:1) Excised root respiration did not significantly differ after different excision times under three water supply conditions. Excised root respiration declined sharply by 32%-39% after the first 20 minutes. 2) Determination of the changes in δ¹³C isotope ratios in excised roots after different excision times provided us information on how the δ¹³C isotopes ratio changed in the roots of B. ischaemum. The mean value of the δ¹³C isotope ratio after the first 2 h was greatest in the well-watered condition, intermediate under moderate drought stress, and least under severe drought stress. The mean values of δ¹³C isotope ratios first increased and then decreased during the entire period of 0-360 h, with the highest value of 31.46‰ at 216 h. 3) The excised root respiration rate and the δ¹³C isotope ratio were significantly influenced by root area, specific root area, N concentration, C/N ratio, and δ¹³C of root tissue. 4) Moderate drought stress contributed to a simultaneous increase in the root growth rate (C fixation) and root respiration (C metabolic rate).