Abstract: Diagnosis and prevention of kelp disease is the key to ensuring healthy culture of kelp．In order to improve disease diagnosis and prevention level of kelp aquaculture users, expert system of kelp disease diagnosis were studied．Acquisition of knowledge was studied, mainly based on literature published in academic journals, supplemented by investigation of experts, 31 types of kelp diseases were collected and sorted out．Production rules were selected to describe knowledge, and rule base was constructed．Forward reasoning was used for disease diagnosis．The system was implemented by JSP+Sevlet+JavaBean, which could meet needs of kelp aquaculture users for disease diagnosis and prevention, and next research direction and content were pointed out．