[Objectives]  To clarify the immigration pattern and source population of the fall armyworm (FAW, Spodoptera frugiperda) in Henan province, and provide basic information for the allopatric forecasting of FAW. [Methods]  Migration routes of FAW were tracked by trajectory analysis using the WRF4.0 (Weather Research and Forecasting Model) and source areas of immigrants analyzed based on searchlight trap catches at 88 monitoring stations in Henan province in 2019 and 2020. [Results]  Immigrants fly north along two paths; east and west. The eastern route mainly runs from Guangdong and south of Yangtze River provinces from June to August, with a few immigrants from Anhui and Jiangsu from August to September. The western route is the main source of populations invading Henan province. These depart from the southwestern, mountainous, corn belt, including the Yunnan-Guizhou Plateau, eastern Sichuan, Chongqing, western Guangxi, western Hunan and Hubei and southern Shaanxi, and fly 1-3 nights to arrive in central and western Henan in July and August. Weather can cause annual fluctuations in the timing of immigration of the FAW to Henan Province. A case study revealed that long-term and heavy precipitation south of the Yangtze River during mid-to-late June 2020 retarded the takeoff of source populations in southern China, postponing the arrival of immigrants in Henan. [Conclusion]  The density of field populations of FAW in Guangxi and Yunnan in March, and in Chongqing, Guizhou and Hunan in April and May, can be used to predict the number of immigrants that will arrive in Henan. The emergence period in Hunan and Hubei during May and June, and the rainfall in June, are also predictive factors for the arrival of FAW in Henan province.