Global climate change has intensified the uncertainty of precipitation patterns, increased precipitation variations, and profoundly affected the ecosystem multifunctionality (EMF) of semiarid grasslands. However, the relative contributions of biotic and abiotic factors to EMF under precipitation changes and their mechanisms remain unclear. We conducted a precipitation manipulation experiment initiated in 2013 in the grasslands of the Loess Plateau, and measured ecosystem properties in 2023 after ten years of continuous treatment (+40 %, +20 %, and 0 %) to examine how biotic (plant diversity and soil microbial diversity) and abiotic (soil water content and soil pH) factors regulate EMF under different precipitation regimes. The results showed that with the increase in precipitation, EMF significantly increased. The positive correlation between plant diversity and EMF was stronger than that between microbial diversity and EMF. Variance decomposition indicated that abiotic factors, especially soil water content (SWC), explained a much larger proportion of EMF changes than biotic factors (20.1 % vs. 1.1 %). The structural equation model further indicated that precipitation also indirectly enhanced EMF by increasing SWC and plant diversity. Soil microbial diversity indirectly affected EMF by regulating plant diversity. An increase in soil pH value was unfavorable for microbial diversity and weakened EMF to a certain extent. We concluded that SWC and plant diversity are the key abiotic and biotic determinants of EMF in semi-arid grasslands, emphasizing the crucial influence of precipitation and the dominant role of abiotic factors.