Abstract Aims As the largest carbon (C) pool in terrestrial ecosystems, soil organic carbon (SOC) plays a critical role in the global C cycle. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) are two categories of SOC that are based on particle size. Nitrogen (N) addition considerably affects SOC content. However, research on the characteristics of POC and MAOC and their formation mechanisms under N (inorganic and organic N) addition remains unclear. Methods we conducted a meta-analysis based on data from 52 studies on terrestrial ecosystems in China to investigate the responses of SOC, POC, and MAOC contents to N addition and to reveal the formation mechanisms of POC and MAOC. Results The results showed that organic N addition significantly increased the contents of SOC, POC, and MAOC (P < 0.05), while inorganic N addition significantly increased those of SOC and POC (P < 0.05), which was associated with the addition of urea. The POC and MAOC contents increased with the extension of fertilization duration (years); however, the physical stability of SOC remained unchanged. No correlation was observed between the SOC sequestration rate (SOCSR) and duration of fertilization under inorganic N addition, while SOCSR showed a trend of first increasing and then decreasing under organic N addition, reaching a maximum at approximately 10 years. Conclusions The main factors affecting the POC and MAOC contents were microbial biomass carbon (MBC) and soil pH, and the formation mechanisms of POC and MAOC were different under inorganic and organic N additions.