This paper presents results of a research on the effects of steep topography to the values of the spectral bands on the SPOT-5 satellite images and methods of correcting of the terrain effect in the forest timber volume interpretation in Ha Tinh. The author used information on SPOT-5 images, digital elevation model of the points which are 30 meters in Ha Tinh, ground survey data of 197 plots, use statistical analysis methods to build the equation for forest timber volume interpretation from the values of the spectral bands. Research has shown that when the slope over than 10 degrees, average difference in values of spectral bands between the slop directions will be exceed 5 percent and it is need to mitigate the impacts of slope and slope direction to the spectral values in the forest timber volume interpretation and vegetation cover classification in general. Varies of bands red and near infrared between the directions less than othe bands, so use of these bands to construct vegetation cover classification index will reduce affects of the terrain. Interpretation of forest timber volume based on values of spectral bands on the SPOT-5 satellite images has error is about 27 m3/ha for one survey point, 1.6 m3/ha for one commune, 0.9 m3/ha for one district is and 0.3 m3/ha for the province.