【Objective】Microbes and their necromass play a key role in the accumulation and long-term sequestration of soil organic carbon (SOC). Moreover, continuous increases in nitrogen (N) and phosphorus (P) inputs can significantly affect microbe-mediated SOC accumulation processes. The microbial necromass accumulation coefficient (NAC), which quantifies the accumulation of microbial necromass per unit of microbial biomass, plays a key role in assessing the efficiency of microbial necromass accumulation. However, the influence of short-term and long-term additions of N and P on this coefficient within meadow ecosystems remains unclear. This study focused on investigating the differential responses of NAC to (1) short-term and long-term N and P additions and (2) additions of N and P across different soil layers. 【Method】To explore the response of NAC to N and P additions, this study analyzed soil samples from the meadow on the Qinghai-Tibet Plateau subjected to 1 year (short-term) and 10 years (long-term) of N and P additions. It was measured the soil microbial necromass carbon (MNC) and the soil microbial biomass carbon (MBC), and calculated the value of NAC. Additionally, considering other environmental factors including soil physical and chemical properties, microbial extracellular enzyme activities, and plant biomass, the main influencing factors of NAC were identified. 【Result】The results showed that after short-term N and P additions, the NAC values in the 0-10 cm and 20-30 cm soil layers were 31.33±2.97 (mean±SE) and 38.12±3.90, respectively, and N and P additions had no significant effect on NAC (P>0.05). After long-term additions of N and P, the NAC values in the 0-10 cm and 20-30 cm soil layers were 14.46±1.12 and 17.49±3.22, respectively; and the additions of N and P significantly reduced the NAC in the 20-30 cm layer (P<0.05). The results of the Random Forest indicated that pH was the most important factor affecting NAC, and the correlation analysis revealed a significant positive relationship between soil pH and NAC. Moreover, the long-term N addition, P addition and simultaneous addition of N and P significantly reduced the pH of the 20-30 cm soil layer. These findings suggest that the decrease in soil pH due to long-term N and P supplementation is the main cause of the reduction in NAC. The lowered soil pH may lead to the dissolution of minerals, thereby reducing the mineral protection of MNC, making it more susceptible to decomposition, ultimately decreasing the NAC of microorganisms. 【Conclusion】In summary, changes in pH resulting from long-term nutrient additions dominated the changes in NAC. In the context of ongoing increases in N and P deposition, it is advisable to closely monitor changes in soil pH and implement timely measures to maintain the stability of SOC. This study explores the differential responses of NAC to N and P additions and their influencing factors, providing data support for understanding microbial-mediated carbon accumulation under the context of increasing N and P deposition.