Genetic diversity within and among 11 geographic populations of the beet webworm Loxostege sticticalis across five provinces in the northern part of China were evaluated using amplified fragment length polymorphism (AFLP) analysis. Five AFLP primer combinations were used on 88 L. sticticalis samples from different locations, detecting a total of 384 polymorphic and 27 monomorphic fragments. Although extensive genetic diversity occurs among individuals from different geographic populations (P = 93.4%, h = 0.398, I = 0.572), the majority of the genetic diversity is within populations and not between populations (G_ST = 0.196), which agrees well with the results of analysis of molecular variance (84% of the total genetic variation is within populations), indicating high gene flow (N_M = 2.046) among natural populations, which are not genetically differentiated. L. sticticalis in northeastern China, northern China, and northwestern China are part of a single large metapopulation. Cluster analyses based on AFLP data were preformed to graphically show groupings between individuals and between populations. Individuals from the same region were not grouped together very well. Eleven subpopulations were clustered into six broad groups, and there was no significant correlation between geographic distance and genetic dissimilarity (r = 0.1236, P = 0.8512). Principle component analysis also indicated a lack of genetic differentiation between the 11 populations. These results indicated that, although high genetic variability existed among individuals, there was little genetic differentiation among geographic populations, which can be explained by the effects of long distance migration of the beet webworm in China and consequent gene flow.