Since 2018, increased infestation by the fall armyworm Spodoptera frugiperda (FAW), an invasive pest worldwide, has negatively affected Asian crop production. Seasonal migratory activities drive regional outbreaks of this pest, but it remains unclear whether there is direct transboundary movement between East Asian and South Asian regions. From 2019 to 2023, FAW moth movements were monitored in Ruili of Yunnan Province, a city at the border area of China and Myanmar which is located in the insect migratory route between China and South Asian countries such as India and Bangladesh. The results showed that there was regular seasonal migratory activity of the pest, which could be divided into spring–summer (April–June) and autumn (October) peak migration periods. Further analysis using trajectory simulation model indicated that the FAW moths in spring–summer migration mostly come from Myanmar, the northeastern states of India and Bangladesh, and returns to the three countries in autumn from Southwest China. Our study clarifies the regional migration pattern of the FAW moth in China and South-Southeast Asia, providing a theoretical basis for constructing a regional early warning and management systems of this pest.