In the practice intersatellite optical communication (IOC), the method of multi-field scanning is needed to capture the goal satellite. And the scanning range is a key parameter of multi-field scanning, so the precise study of it is needed. Based on the constructed theoretical single-field scanning model, the theoretical analysis has been preceded and a theoretical model of multi-raster scanning has been founded too. According to this model, the results of analysis proved that there is an optimization in the selection of scanning range, in order to achieve a shortest acquisition time. And for the convenience in practice, a numerical simulation has been carried on. With the presented simulation results, an experimental formula to choose the optimum scanning range in multi-raster scanning has also been proposed.