Many research works indicate that the topographic factors have strong influence on forest canopy reflectance. However, the quantative effects of canopy reflectance by topographic is difficult to be evaluated. For this purpose, the topographic effects on sloping forest reflectance are quantitatively evaluated based on GOST model and the observed remotely-sensed images. The major findings are summarized as follows: First, the topographic factors (slope and aspect) have great impacts on sloping canopy reflectance. A case study shows that the modeled topographic index for reflectance ([bidirectional reflectance distribution of a sloping forest-bidirectional re- flectance distribution of a flat forest]/bidirectional reflectance distribution of a flat forest), which is the relative error in modeled canopy reflectance by ignoring the topographic effects, can reach up to 58%, while the maximum observed topographic index for reflectance varies from 0.012 to 0.038. Second, model simulations show that topography has different effects on the sloping canopy reflectance in different view directions. These effects should be considered in analyzing multi- angle images. Third, topographic factors have different impacts on sloping canopy reflectance of different canopy structures. Canopy structure should also be considered in topographic correction on reflectance images because topographic factors alone is insufficient for correcting all variations of reflectance with slope and view angle.