Insect is an important component of forest biodiversity, which is closely related with plant in the main community of forest ecosystem. Intimidation of forest pest and variation of insect diversity is of importance for assessing forest ecosystem health. Insect diversity can be used for rapidly assessing forest ecosystem health. For example, indicator insects have been used to evaluate toxicity levels, abundance of species, levels of biodiversity, target insect status, and endemism levels for forest ecosystem. With a focus on the important interference factors influencing forest environmental health, this paper clarified the biological and ecological basis for insects to be used as a bio-indicator to monitor and assess forest health. We also discussed the fluctuation of insect populations, especially that of the population of the rare species under the influence of habitat fragmentation, and the density and distribution of the insect population under the influence of air pollution, drought, increased CO2 concentration. Meanwhile, the existing problems to use insects as a bioindicator to monitor and assess forest environmental health were analyzed.