We put forward a new method for buffer generation based on run-length encoding system and raster overlay idea. Firstly, we use a brush whose width equals to the buffer distance to scan and trace the buffer objects from the bottom of raster region, and label the grid which has been scanned and execute the dynamic raster overlay to get the buffer zone in the raster form. Then, we transform the raster data into vector. Considering the obvious deficiency of computational efficiency and memory capability for rater data based on direct encoding, we adopt the run-length encoding method to store the raster data and perform the raster operations based the data structure. In order to enhance the spatial location precision, we suggest to use the float-type data as the mark of edge for run-length unit. Taking the set of linear objects for example, we illuminate the implement steps to generate the buffer zone using the overlay algorithm of run-length brush. The tests and analysis indicate that this method is a fine buffer generation algorithm, which has a general advantage in the time and space complexity and computational precision.