Forest insect populations show some spatio-temporal patterns, and spatial synchrony is the most common one. The properties, causes, and study methods of spatial synchrony of forest insects are reviewed in this paper. Spatial synchrony of forest insects is ubiquitous, but varies among species. Spatial synchrony often decreases with distance, and is related to temporal scale. The Moran effect and dispersal are two of the main mechanisms that explain spatial synchrony, and the Moran effect is usually larger than that of dispersal. Research methods involved in the acquisition of pest occurrence data, the measurement and the causes of synchrony were also reviewed. The reconstructed occurrence history of forest insects using dendroecological analysis can provide reliable data many years after the occurrence, worthy of use as a reference for researchers in China. Both spatial statistics and geostatistical methods are powerful measures of spatial autocorrelation; however, they have not been applied extensively to spatial synchrony studies as they do not deal with multiple samples over a period of time. Variation partitioning, using distance-based Moran's eigenvector maps(dbMEMs) as spatial variables, is a relatively novel method to study the driver of forest insect outbreaks.