Abstract: The structure and diversity of arthropod community in longan orchard were studied. The result showed that there were 102 species of arthropod in longan orchard, they included 54 species of pest, 35 species of natural enemy and 13 species of moderate insect. If judging pest groups by the plant nutrition, Lepidoptera take the first place in the chewing mouthparts pests. Its dominant species were the Conopomorpha sinensis Bradley, Olethreutes leucaspis Meyrick and Conopomorpha litchiella Bradley. The Cornegenapsylla canarium Yang et Li was the dominant species in the piercing-sucking mouthparts pests. The Chrysoperla Sinica (Tjeter), Chilomenes quadriplaglata (Swartz) were the dominant species in the meat nutrition insects group. The Brochymena lasus (Walker), Anastatus japonicus Ashmead and Macrocintrtus addomiulis Fabricius were the dominant species in the parasitical insects group. Analysis on the dynamics of community showed that the indices of the community were obviously fluctuated with time. During the period of June, 29 to Sept, 27, the indices of ecological concentration was low, the diversity and evenness were high. So the structure of arthropod community was rational.