Directional thermal radiation of canopy was studied and the related model was set up. According to the mechanism of radiative transfer, 3D canopy scenes were established and the scenes were discretized by differential cells. According to the observed geometric parameters, the radiative transfer of scatter and emission for every internal cell and among cells was calculated. Finally, the directional thermal radiation of canopy could be retrieved from the integral calculation of all differential bodies in the hemisphere. The existing in-situ data were used to test the 3D radiative transfer model and the simulating results. The correlation coefficients are 0.91 and 0.79, the RMSE are 0.4K and 0.6K, respetively. The results show that the model is effective and it can improve the precision of temperature inversion and realize component temperature inversion.