With frequent occurrence and severe harm of vegetable insect pests, agricultural benefits are reduced and consumer health is threatened because of improper insect pest diagnosis and control measures. The improvement of insect pest control level can guarantee large-scale plantation, high yield and high quality of vegetables, and an insect pest diagnosis expert system can assist in diagnosing insect pests and relieving the contradiction of low quality of agricultural planting personnel and insufficient plant protection experts. Aiming at vegetable insect pest occurrence characteristics, by simulating an analysis mode of insect pest diagnosis of plant protection experts, fully considering ways of thinking of users and adopting a case-based reasoning mechanism, an insect pest diagnosis expert system constructing method comprising contents of new case generation, case library construction, insect pest symptom weight calculation, case retrieval and match, human-machine interactive interface and the like is created and a vegetable insect pest diagnosis expert system taking the method as a core is constructed. Moreover, due to an online edition, a standalone version and a personal digital assistant (PDA) version of the vegetable insect pest diagnosis expert system, multi-channel insect pest diagnosis information technical service is provided for users with different requirements.