Microbial necromass plays a key role in maintaining the storage and stability of soil organic carbon (SOC). The fundamental roles of microbial functional traits in regulating microbial necromass have been recognized in numerous studies. However, the interactions across multitrophic levels (including bacteria, fungi and nematodes) represent an important but still incompletely understood pathway linking microbial dynamics to necromass accumulation, particularly under nitrogen (N) deposition. Here, we investigated the soil microbial necromass carbon (MNC) contents during 7-year N addition experiment conducted in two typical alpine coniferous plantation forests and explored the associations of microbial functional traits and multitrophic traits with soil MNC accumulation under N addition. Our findings revealed that N addition promoted MNC accumulation and increased the microbial r/K ratios, bacterial rrn copy numbers and multitrophic network complexity. The MNC contents were positively correlated with the microbial r/K ratios, rrn copy numbers and multitrophic network complexity. Structural equation modeling suggested that N addition increased the multitrophic network complexity and changed microbial life strategies (increased microbial r/K and bacterial rrn copy numbers) through soil nutrients, which was associated with higher MNC contents. Collectively, our findings demonstrate that the promoting effects of N addition on MNC accumulation were jointly associated with microbial life history strategies and multitrophic network complexity. These findings provide novel insights into the conceptual linkage underlying the positive effect of N deposition on soil C sequestration through increased MNC and emphasize the importance of integrating microbial life history strategies and multitrophic interactions into soil carbon cycling models.