Response of the eco-physiological characteristics to simulated photosynthetic radiation intensity in Stipa bungeana , A rtemisia sacrorum , Stipa grandis , A neurolepidium dasystachys leaves was investigated.Results showed that with increasing irradiation , Photosynthetic rate( Pn) was increased in lower density irradiation , but was reduced in higher density irradiation.transpiration rate( Tr) rate was enhanced with increasing irradiation.WUE for Stipa bungeana rose with increasing irradiation at first and then declined despite the intensified irradiation.WUE for Stipa grandis , A rtemisia sacrorum , and A neurolepidium dasystachys were enhanced with irradiation gradually.With growth midseason , Pn and WUE of the four species reached a maximum in July and a minimum in September , while Tr reached a maximum in August.The species ranked in the descendant order of A rtemisia sacrorum , Stipa grandis , A neurolepidium dasystachys , and Stipa bungeana in terms of the max Pn ; in the descendant order of Stipa bungeana , A neurolepidium dasystachys , Stipa grandis , and A rtemisia sacrorum in terms of Tr ; and in the descendant order of A rtemisia sacrorum , A neurolepidium dasystachys , Stipa grandis , and Stipa bungeana in terms of WUE.The chlorophyll fluorescence parameter indicated that the conversion efficiency of primary light energy under light ( Fv’/Fm’) of PSII , actual PSII efficiency (PhiPSII) , and PhiCO₂ declined in line with the CO₂ concentration , but the nonphotochemical quenching coefficient (NPQ) ascended.