External cooling technology is one of the key technologies to realize fast cast rolling process of aluminum, i.e. using compulsive cooling on the outside surface of plate and rollers to attain the aim of improving the cooling ability of system, increasing cast rolling speed, enhancing aluminum plate quality. This paper analyzed the influence of external cooling surfaces of the board and the roller on the temperature field of the roller and the board as well as cast rolling speed, based on the researching heat transfer model of cast rolling process and the characteristics of roll plate system temperature field. It is shown that, with the increase of cast rolling speed, the influence of cooling board surface on increasing cast rolling speed is gradually decreasing, while the influence of cooling roller surface on increasing cast rolling speed is gradually increasing. The reason for this phenomenon lies in the different mechanisms for improving cast rolling speed of external cooling plate surface and roll surface. Therefore, external cooling of rollers surface should be regarded as the developing direction of external cooling technology; through applying high efficiency external cooling media and rationally setting up external cooling area, the requirement of fast cast rolling process for the external cooling technology might be satisfied. The research is very important in working out external cooling technology scheme.