A systematic understanding of the changes and influencing factors in soil microbial necromass carbon during the restoration process of artificial forests is crucial for evaluating the soil carbon sink of these forests. This study focuses on artificial Robinia pseudoacacia forests of varying restoration ages (14 years, 20 years, 30 years, and 45 years) and the adjacent sloping farmland in the hilly area of the Loess Plateau. Employing biomarker technology, this study clarified the accumulation of soil microbial necromass carbon and the efficiency of the microbial carbon pump, and unveiled microbial life history strategies through metagenomic sequencing. The key driving factors of soil microbial necromass carbon accumulation and microbial carbon pump efficiency were also investigated. The results showed that with the increase in the restoration years of Robinia pseudoacacia forests, soil microbial necromass carbon exhibited an increasing trend, while microbial carbon pump efficiency showed a decreasing trend. This indicates that during the restoration process of Robinia pseudoacacia forests, the accumulation effect of soil microbial necromass carbon is enhanced, but its contribution to soil organic carbon shows a decreasing trend. The results of the random forest model showed that, besides soil nutrients and moisture, soil microbial life history strategies are key driving factors regulating microbial necromass carbon accumulation and microbial carbon pump efficiency. Specifically, soil microbial carbon pump efficiency was positively correlated with S-strategy microbes and negatively correlated with A-strategy microbes. Further analysis revealed that damage repair genes and osmoregulation genes in S-strategy microbes were two important predictors of microbial carbon pump efficiency variation, while lipid genes and lignin genes were predictors in A-strategy microbes. Overall, this study clarified the trend changes in soil microbial necromass carbon and microbial carbon pump efficiency during the restoration process of artificial forests and revealed the key driving factors through soil microbial life history strategies.