To investigate the physiological response mechanisms of important economic herbaceous plants used in vegetation restoration in arid regions under drought stress,the annual herbaceous plant Corispermum squarrosum as the research object.Through pot experiment on water control,four different soil moisture treatments were established:control (CK),light drought (LD),moderate drought (MD),and extreme drought (ED).The soil moisture contents under these treatments were (90±5)%,(70±5)%,(50±5)%,and (30±5)%,respectively.The changes in gas exchange parameters and chlorophyll fluorescence parameters of Sami leaves under drought stress were analyzed..The results showed that:1)The photosynthetic physiology of C.squarrosum was insensitive to light drought.Compared with the CK,only the stomatal conductance(Gs)and the actual photochemical efficiency(ΦPSII)in the LD were significantly reduced by 22.86% and 22.09%,respectively.2)Under the MD,C.squarrosum primarily exhibited significant gas exchange limitations.Compared to the CK treatment,the net photosynthetic rate(Pn),Gs,transpiration rate(Tr),and ΦPSII decreased significantly by 61.04%,42.86%,62.50%,and 39.13%,respectively.While other parameters showed no significant difference between the CK and MD treatments.3)Under the ED,the gas exchange characteristics of C.squarrosum underwent significant changes.Compared to the CK treatment,gas exchange parameters Pn,Gs,and Tr in the ED were significantly reduced by 77.06%,60.00%,and 81.25%,respectively,whereas the water use efficiency(WUE)increased by 19.33%.For chlorophyll fluorescence parameters,the maximum photochemical efficiency(Fv/Fm),ΦPSII,and photochemical quenching(qP)decreased significantly by 28.24%,65.22%,and 54.84%,respectively.The reduction in Photosystem II activity was identified as the primary factor leading to the decrease in net photosynthetic rate under the ED treatment.Elucidating the changing characteristics of gas exchange and chlorophyll fluorescence parameters in C.squarrosum provides a solid theoretical basis for the selection of improved plant materials and vegetation restoration practices in arid and semi-arid regions.