With extensive application of computer technology and 3S(GIS、RS and GPS) in agriculture, traditional agriculture is turning into precise agriculture, and hence an agricultural expert system comes into being. Aimed at the status quo of soil nutrition management and fertilization technology, this paper probes into how to design a soil and fertilizer expert system based on the factors of soil fertility, fertilization and crop, and by adopting advanced technologies such as object-oriented programming (VB), database (Access) and 3S. This kind of expert system can not only guide farmers in applying fertilizers rationally, but also provide manager and businessman with decision-making service. so it is of high practicability and high extension value, and will create good economic and social benefits expecially in the lakeside plains.