Abstract: Based on the data measured with Licor-188B radiation-quantum-illum-ination analyzer， a numerical model to simulate the extinction coefficient of winter wheat canopy was established．Validation of the model showed that the model could simulate extinction coefficient fairly well with higher significant levels．Numerical analysis with the model suggest that the extinction coefficient of direct solar radiation is much higher than that of scattered radiation．The daily extinction coefficients of winter wheat canopy are enhanced with latitude increasing with a variation from 0.6865 to 0.6969 in Huang-Huai-Hai Plain of China in heading stage．