Abstract: Taking winter wheat (Triticum aestivum L.) as material, crop water stress index (CWSI) was calculated by using two methods: Jacksons theoretical model and Jones simplified model with the technology of the visible and thermal infrared imagery under different irrigation schedules. The validity and feasibility of Jones method for monitoring winter wheat water stress in the North China Plain (NCP) was briefly analyzed refer to theoretical CWSI. The results showed that CWSI calculated by the two models had closed relationships with the soil moisture conditions of the main root zone soil profile under 6 irrigation schedules. Moreover, Jones method was more sensitive to the subtle changes of crop water status and had a better response to the changes in stomatal conductance of winter wheat.Threshold values of CWSI were determined initially for maximizing the yield of winter wheat based on two different models. The results indicated that Jones simplified model was a practical and reliable method for monitoring crop water status, which could be used to establish a readily portable system for spot measurements in crops and guide irrigation scheduling accurately.

Key words: Winter wheat, Canopy temperature, Crop water stress index, Dry reference leaves, Wet reference leaves