In order to explore the accumulation of soil microbial necromass carbon (MNC) in different grassland types, and determine the contribution of MNC to soil organic carbon (SOC) and its influencing factors. In this study, we measured soil physicochemical properties, microbial community and soil amino sugars contents through the biomarker method in 0-20 cm soil layers of Meadow steppe (MS), Typical steppe (TS), Desert steppe (DS), Steppe desert (SD) and Desert (D) in Ningxia, and further analyzed the relationship between MNC and soil physicochemical properties and microbial community. Our results indicated that: the contents of soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), fungi, bacteria, actinomycetes and protozoa in MS and TS had significantly higher other grassland types (P ＜ 0.05). The contents of glucosamine (GluN), mannosamine (ManN), galactosamine (GalN), muramic acid (MurA) were the highest in MS, and the lowest in D (P ＜ 0.05). The content of GluN ((0.62±0.18) μg/mg) in different grassland types was the highest, and the content of MurA ((0.04±0.01) μg/mg) was the lowest. The contents of bacterial necromass carbon (BNC), fungal necromass carbon (FNC) and total necromass carbon (TNC) in different grassland types varied 0.12-5.74 μg/mg, 0.22-15.31 μg/mg and 0.34-21.05 μg/mg, respectively. The contribution of BNC, FNC and TNC to SOC in different grassland types varied 9.0%-17.8%, 22.0%-48.2% and 33.5%-66.0%, respectively. We found that the contribution of MNC to SOC was 1.3-3.8 times higher in FNC than in BNC. The correlation analysis showed that MNC was significantly positively correlated with elevation, MAP, AI, AGB, BGB, SOC, TN, NH₄⁺-N, NO₃^--N, TP and microbial biomass (MBC, MBN, MBP, fungi, bacteria, actinomycetes and protozoa), and significantly negatively correlated with MAT, BD and pH. The content of BNC and FNC increased with the increase of bacteria and fungi, respectively (P ＜ 0.001). The content of TNC increased with the increase of fungi/bacteria ratios (P ＜ 0.05), and decreased with the increase of GP/GN ratios (P ＜ 0.01). The random forest analysis showed that the different importance of climate, plant and soil factors on the MNC. In conclusion, the variation in grassland types altered soil physicochemical properties and microbial community, resulting in more beneficial to the formation and accumulation of FNC, and TN and pH were the main influencing factors of MNC. Thus, this study can provide data support for further research on the microbiological mechanism of SOC sequestration in arid and semi-arid grassland ecosystems.