The applications of remote sensing to hydrology, which can roughly be divided into the direct remote sensing applications and the indirect remote sensing applications, have been extended in last a few decades.  However, its spatial and temporal resolutions of remote sensing information, together with the complex issue of hydrological scales, have double roles to applications of remote sensing on hydrology.  In one side, they meet difficulties because of different spatial and temporal scales; on the other side, they bring new techniques to hydrological scale issues and this will definitely promote the development of hydrology, such as the development of global hydrology.  This paper approaches the spatial scale issue of remote sensing hydrology from four aspects: hydrological process mechanisms at varied scales, spatial resolution of remote sensing information, hydrological parameters gathered at one scale to be used in making predictions at other scale, and the development of hydrology with the aid of remote sensing.  The expansion of instantaneous remote sensing information to a long time scale and temporal resolution of remote sensing information are discussed with temporal scale issue taking into account.