Rainfall, particularly in continental climates with a monsoonal tendency, impacts the microbial niches during mountain-cultivated ginseng growth. With microbial community shifts, ginseng diseases cultivated and protected under rain-shelter cultivation may ultimately be altered. Such cultivation may influence microflora dynamics via meteorological parameter variations; however, this is unclear yet. The present study found that rain-shelter cultivation affects the distribution of fungal communities within the mountain-cultivated ginseng. This led to an improved community structure in the ginseng rhizosphere, characterized by the proliferation of antagonistic fungi and a reduction in pathogenic fungi. Alternaria, the pathogen of black spot, has exhibited larger differences, reaching more than 2 times during the flowering period and 4 times during the withering period. The correlation analysis of meteorological factors indicates that soil temperature and humidity are the primary meteorological factors that affect mountain-cultivated ginseng. It is evident that rain-shelter cultivation regulated the microecological environment of the mountain-cultivated ginseng rhizosphere and resulted in positive outcomes. The disease investigation supports this point; the number of main diseases under rain-shelter cultivation was lower than those under open-field cultivation. The incidence of ginseng root diseases, such as rust rot and root rot, was reduced by 5–6%. And the incidence of ginseng leaf diseases, including gray mold and black spot, was reduced by 5–10%. This research provides evidence to address the dynamics of microbial ecology under rain-shelter cultivation and its benefits for sustainable mountain-cultivated ginseng management.