Abstract: To address the complexity of the traditional Crop Water Stress Index (CWSI) calculation and its limited applicability for rapid and convenient water status assessment, this study investigated winter wheat to analyze the diurnal variations in canopy temperature and canopy–air temperature difference under different irrigation treatments during key growth stages. A simplified empirical CWSI model was developed, and the feasibility of using CWSI to predict the water status of winter wheat was evaluated. The results showed that: (1) both canopy temperature and canopy–air temperature difference effectively reflected differences in the water status of winter wheat. Higher soil moisture resulted in lower canopy temperature and canopy–air temperature difference, whereas lower soil moisture led to higher values. (2) A lower baseline was established by regressing the canopy–air temperature difference against vapor pressure deficit (VPD), and the theoretical maximum canopy–air temperature difference was adopted as the upper baseline to develop a simplified empirical CWSI model. The CWSI values calculated by the simplified model exhibited diurnal variation patterns consistent with those obtained from the Idso empirical model and the theoretical model, with highly significant positive correlations (P < 0.01), demonstrating the feasibility of the proposed simplified model. (3) The CWSI values calculated by both the simplified empirical model and the theoretical model increased with increasing soil water suction, whereas the simplified empirical model was more sensitive to changes in crop water status. (4) Regression analysis indicated that the CWSI derived from the simplified empirical model was significantly (P < 0.05) or highly significantly negatively correlated with winter wheat leaf water content and the mean soil water content within the 0–60 cm soil layer. Higher CWSI values corresponded to lower leaf water content and soil water content. Moreover, the prediction model based on CWSI achieved higher accuracy for leaf water content than for soil water content, indicating that CWSI is more effective in characterizing crop water status. Based on the experimental results, a CWSI value of 0.6 is preliminarily recommended as the upper irrigation threshold for the simplified empirical model in winter wheat. Overall, the proposed simplified empirical CWSI model exhibited good reliability and sensitivity, and the corresponding prediction models effectively estimated crop and soil water status, providing a scientific basis for winter wheat water status monitoring and precision irrigation management.