In order to overcome the disadvantages of inconvenience and low accuracy of keywords spitting search, and artificial answer delay for the online messages in the current agricultural consulting system, this paper proposes a solution which complement the advantages of automatic question answer with expert real-time answer. Firstly, vector space model was improved by semantic extension and feature item weight modification. And then, based on the agricultural technical information database and expert team, an agricultural science and technology consulting system was developed by the Ajax. To the simple natural language questions, the system answers it automatically through improved vector space model in automatic question and answer. To the complicated question, the agricultural experts gave answer immediately after chatting with inquirer on line in expert real-time answer. The experiment show that the system has features of accurate and rapid reply, professional answer and high satisfactions. It can better meets the need of agricultural production techniques.