A rapid increase in nitrogen deposition has caused many hazards to the Tibetan Plateau over the past few decades. However, as one of the important limiting factors in alpine ecosystems, nitrogen fertilizers are often used to restore the severely degraded grassland. But, little is known about the response of soil microbes to nitrogen addition in the western Tibetan, which will limit our understanding and comprehensive assessment of global alpine grassland ecosystems. This study conducted an experiment with five levels of nitrogen addition (0, 5, 10, 20, 40 g N m⁻² y⁻¹) in an alpine steppe (AS) and an alpine desert steppe (ADS) at the source of Brahmaputra. In this study, plant and soil data were analyzed from August 2023, it showed that nitrogen sensitivity of soil microbes and their response to nitrogen addition vary with the nitrogen addition rate, grassland type, microbial kingdom, and the dimension used. Nitrogen sensitivity of soil bacterial community in the AS was higher than that in the ADS at 10 g N m⁻² y⁻¹ nitrogen addition rate, while the result was reversed at 20–40 g N m⁻² y⁻¹ ; the fungal community was more sensitive than bacterial community in the ADS at 5 g N m⁻² y⁻¹ nitrogen addition rate, while the result was reversed 20–40 g N m⁻² y⁻¹ ; the nitrogen sensitivity of the bacterial community's β-diversity in AS varied across species, functional, and phylogenetic dimensions. The main environment factors affecting nitrogen sensitivity were different in the AS and the ADS. This study explored the effects of nitrogen addition on soil bacterial and fungal communities in two types of grasslands in the western Tibetan, providing important foundations for further understanding of microbial ecology in alpine ecosystems, as well as valuable insights for managing nitrogen deposition in alpine ecosystems.