Sogatella furcifera (Horváth) is a migratory rice pest that periodically erupts across Asia, and early immigration is an important cause of its outbreak. The early immigration of S. furcifera into southern China shows evident annual fluctuations. In the spring of 2012, the huge size of the immigrant population and the large number of immigration peaks were at levels rarely seen prior to that year. However, little research has been done on the entire process of round-trip migration to clarify the development of the population, the long-distance migration and the final eruption. In this study, the light-trap data for S. furcifera in southern China and Vietnam in 2011–2016 were collected, and the trajectory modeling showed that the early immigrants to southern China came from the northern and central Vietnam, Laos, and northeastern Thailand. Analysis of the development of the population, the migration process and meteorological factors revealed the reasons for the huge size of the early immigration: 1) the expansion of the source area could be seen as a precondition; 2) the large size of the returned population in the last autumn and the warm temperature of southern Vietnam and Laos in the last winter increased the initial populations; 3) the sustained strong southwest winds were conducive to the northward migration of the population during the major immigration period in early May. Therefore, the large-scale immigration of S. furcifera to southern China in the spring of 2012 resulted from the combined effects of several factors involved in the process of round-trip migration.