Agricultural development depends on agricultural innovation, and comprehensive understanding about agriculture development must be conducted from the system perspective. Based on the innovation theory and the integration of sectoral innovation systems theory and induced innovation theory, this paper proposes a new model of agricultural innovation system. The author believes that to analyze the agricultural innovation system must pay attention not only to its structure essentials (resource endowment, knowledge base and technology, actors and network, institution and demand), but also to its function achievement (7 key processes in agricultural innovation system, i.e. knowledge development, resource mobilization, market formation, impact on research direction, entrepreneurial experimentation, institutionalization, development of external economy, and their actual performance). The influence factors of agricultural innovation system include its structural elements, operating mechanism, and external surrounding. The development of agriculture innovation system requires identifying mechanism that blocked its development; finding out relevant policy; and constantly adjusting its structural elements and operating mechanism.