Plants often experience both drought and salinity stress in arid environment. Various mathematical water uptake models exist for plants response to combined drought and salinity stress. The reduction functions are classified as additive, multiplicative and conceptual models. In this study six different macroscopic reduction functions, namely; Van Genuchten (additive and multiplicative), Dirksen et al., Van Dam et al, Skaggs et al and Homaee were evaluated. The experiment was carried out on Rowshan variety of wheat crop in a factorial split plot design with 3 replicates in the Research Field of university Birjand.