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Abstract. The Northeast China Plain (NECP) is one of the main maize (Zea mays L.) production regions in China but is now subject to drought because of climate change and a rain-fed cultivation system. A two-year experiment was conducted in a typical maize cultivation region in the NECP to investigate the responses of plant physiological factors and evapotranspiration (ET) to water stresses at different growth stages, then propose reliable methods to evaluate the crop water stress status. Results show the responses of plant growth and physiological factors to water stress can be divided into three levels based on soil water content (SWC) in the main root zone: when SWC was greater than 0.22 cm^-3cm^-3, stomatal conductivity (g_s) and ET reached their highest values, and the canopy temperature (Tc) was close to the air temperature; when SWC was within 0.15-0.2 cm³cm^-3, the g_s and ET decreased, and Tc increased as SWC decreased; and when SWC was lower than 0.15 cm³cm^-3, g_s and ET reached their lowest values and Tc was greater than 1.2 times the air temperature. Therefore, the ratio of canopy to air temperature of 1.2 can be used as an index to identify a severe water stress status in the study region.