Global environmental changes continuously result in plant migration from lower elevations or latitudes into alpine or arctic tundra ecosystems. In response to global environmental changes, the alpine shrubby tundra on the Changbai Mountain in northeastern China has been invaded by a low-elevation herb species Deyeuxia angustifolia over the past several decades. In this experiment, we studied the effects of D. angustifolia migration, Nitrogen (N) deposition (ambient N vs. N-addition of 10 g/m²/yr), and elevation (a higher elevation of 2200 m vs. a lower elevation of 2050 m a.s.l.) on soil properties and soil microbial communities to better understand the consequences of this migration for soil microbes and obtain feedback on the likelihood of further migration. We found that the migration of D. angustifolia decreased the soil available phosphorus (AP) and microbial biomass (particularly the biomass of Gram-positive bacteria (Gp) and Actinobacteria) at 2200 m a.s.l. N addition enhanced the availability of soil N, the nitrogen: phosphorous (N: P) ratio, and reduced the fungal: bacterial (F: B) ratio at 2200 m a.s.l. There was a higher Gram-positive: Gram-negative bacterial (Gp: Gn) ratio at 2200 m a.s.l. than those at 2050 m a.s.l. Our results suggest that the upward migration of D. angustifolia into the shrubby tundra combined with N deposition will substantially change the soil microbial community composition on the one hand, and result in a shortage of soil P on the other hand, especially at higher elevations. These changes may increase the competitive ability of D. angustifolia, and further benefit its migration, and suppress the shrubby species that currently exist in that habitat. This study helps to understand the mechanisms for the upward migration of D. angustifolia and facilitates the management of the Changbai alpine tundra in a changing world.