In order to explore the atmospheric dynamic mechanisms of the rice leaf roller Cnaphalocrocis medinalis Guenee catastrophic immigrations, the tempo-spatial patterns of its populations occurred in China in 2003 was analyzed topographically under the assistance of ArcGIS. Based on this analysis, two typical great immigrating events were selected. The observational meteorological data and T213 numerical simulation products covering these processes were extracted from the data received by a PCVSAT^TM (PC Very Small Aperture Terminal). These data were input into the model MM5 32 (The Fifth-Generation Mesoscale Model for version 3.2), and a set of atmospheric dynamical fields during these migrating and landing processes were simulated numerically and analyzed objectively. The results were as follows: (1) It was feasible to use the directions of air streams on the 850 hPa (approximately 1 500 m) and 925 hPa(around 750 m) to describe the flight directions of rice leaf rollers in the main migrant layers during the northward and southward migrations of their populations, respectively. There were relatively coincident air streams with a northern exposure during the migration northward of rice leaf rollers and there were concurrent airflows with a southern exposure during the migration southward. The regions with cyclonic curvatures were advantageous to taking-off and emigration of the leaf rollers, and the areas with anticyclonic curvatures were favorable to immigration and landing. (2) The driving effect of the subsiding airflow on the vertical velocity field was most direct atmospheric dynamical mechanism for immigration and landing of rice leaf rollers. When they immigrated into the endangered regions, on the 850 hPa over these regions in 36-12 hours before landing, there were relative strong and wide subsiding airflows. (3) On the divergence fields of 850 hPa and 925 hPa in 36-12 hours before the pest immigrated into the endangered areas, there were conformably positive and high divergence values over the landing regions. This indicated that there were obvious strong sinking airflows over these regions, and these airflows were available for the pest's landing. (4) The diagnostic distributions of horizontal air stream field, vertical velocity field and divergence field on 850 hPa and 925 hPa would provide with good indicative significance for the forecast of rice leaf rollers' immigration and landing.