Based on “On Construction of Agricultural Information System Engineering”，the development of agricultural information science which is the basis of the discipline of agricultural information system was discussed from its science, technology and application background. The agricultural information science was defined as an agricultural science system which is based on modern mathematics, aerospace technique and computer technique, and studing on the information of agricultural production activities, its environmental resources and social economy. It take agricultural science and geo-science theory as its basis. It collects, processes, in-terprets, stores, and transports agricultural information which has dear normal and spatial scale and location using remote sensing technique, geographic information system technique, global positioning system technique and computer net system technique. The theoretical mechanism, technological system, service object, function and component of agricultural information science were put forward. At last, the agricultural information technological system which is composed of satellite remote sensing technology, geographic information system technology, global positioning system technology and computer net system technology and its function were introduced simply.