In order to find out the adaptability and coping strategies to arid environment of Apocynum venetum and A.cannabinum,water physiological characteristics and daily dynamics of photosynthetic characteristics were studied under drought stress.The results showed that:(1)With the advance of drought stress,the leaf water content and relative water content for both Apocynum decreased gradually,and A.venetum decreased greatly compared with A.cannabinum.In the same soil water grade,the leaf water content and relative water content of A.cannabinum were significantly higher than that of A.venetum,but water saturation deficit was lower than that of A.venetum.Under the different soil water contents,the relative water content of leaves in vitro of A.venetum sharply declined after two hours,and declined significantly higher than that of A.cannabinum (P<0.01);After 8 hours,the relative water content of leaves in vitro of A.cannabinum were maintained at higher level.(2)Under treatments of saturated water supply (CK),light drought stress (LS) and moderate drought stress (MS),the diurnal curves of the net photosynthetic rate (P_n),transpiration rate (T_r) and stomatal conductance (G_s) of A.venetum and A.cannabinum were “doublepeak”,while “singlepeak” under severe drought stress (SS).Compared with CK,the subpeak of P_n delayed to about 16:00 under LS and MS condition.The order of P_n and WUE of A.cannabinum were LS>CK>MS>SS,while were CK>LS>MS>SS in A.venetum,and the difference reached to the significant level (P<0.05) except for WUE index between CK and T₁ of two Apocynum.The P_n and WUE of A.cannabinum were significantly higher than that of A.venetum in same soil water grades;The daily average value of P_n and WUE in A.cannabinum were 2.28 μmol·m^-2·s^-1 and 1.41 μmol·mmol^-1,respectively.However,the A.venetum.dropped to 0.29 μmol·m^-2·s^-1 and 0.16 μmol·mmol^-1 under SS conditions.All these reflected that A.cannabinum was with higher water conservation and photosynthetic production capacity than A.venetum,and suitable to plant in Ningxia.