The meadow moth (Loxostege sticticalis L.), in the family Crambidae, is a worldwide pest that is mainly distributed in arid areas of the northern temperate regions. It is one of the most serious migratory pests in the northern farming and pastoral areas of China. Ascertaining its patterns of migration and population expansion and tracking the routes by which it enters China from neighboring nations could provide a scientific basis for forecasting the moth's movements and effectively controlling this economically damaging pest. In this investigation, we carried out a long-term monitoring of the pest around the western suburbs of Xilinhaote City, Inner Mongolian Autonomous Region of China, between 1 June and 17 September in 2010. The study included: the use of a vertical-looking radar (VLR) combined with a searchlight, light-trapping on the ground, assessing the ovarian developmental status of female moths captured at the light traps at different periods, estimating the source areas of the second generation of meadow moth by backward calculating their trajectory, and analyzing how the atmospheric circulation patterns influenced their migrations. The stage of ovarian development was used to determine whether the moths were local or immigrants and to determine whether they were capable of emigrating. We estimated the source areas of the second generation meadow moth's populations to determine where the pest came from. By analyzing the atmospheric circulation patterns influencing the moth migrations, we can predict whether the populations in the source area have suitable conditions to migrate to the monitoring area. The results showed that there was a migration peak of the second generation meadow moth from 8 August to 21 August into the Inner Mongolian pastoral areas, and the date of greatest migration was on 11 August. The search light trapped 9,167 individual meadow moths on this day, and the ovaries of the female meadow moths were mainly in developmental stage I or II, typical of migratory insects. The VLR echoes of the pest populations mainly appeared at a height of 300-400m. The trajectory analysis of the migrations for 12 hours showed that the migrating meadow moths during this migration peak came from the southeast of Mongolia and from the border region between China and Mongolia. The pest populations were conveyed from the source areas to the Xilinguole pastoral areas by air currents from the north-west that prevailed on the south-west side of a Mongolian cyclone, and the moths ultimately immigrated into the Hulunbeier Steppe due to an airstream from the south-west. Usually, atmospheric weather patterns control the flight of the meadow moth; areas of precipitation or subsidence are very favorable for the moths dropping to the ground. As long as there is airflow from southern Mongolia to the pastoral areas of China, meadow moths will be able to migrate into China, although their destinations will depend on variations in the direction of the weather currents. In this study, we showed that the atmospheric conditions were extremely favorable for meadow moths to migrate from Mongolia and land in China and are the predominant cause of this migration. The movement of meadow moths into the pastoral regions of China could be disastrous.