Interplanting is an important measure during the management of Cunninghamia lanceolata (Chinese fir) plantation. Phosphorus is one of the main limiting nutrient elements in the forests of southern China, but the effect of interplanting model on soil phosphorus is not clear. In this study, soil phosphorus fractions in surface soil (0-10 cm) were determined in different interplanting forests (young Chinese fir interplanting forest, mature Chinese fir interplanting forest) and young pure Chinese fir plantation. The results showed that:(1) Interplanting forests showed increased soil total phosphorus (including organic and inorganic phosphorus), microbial biomass phosphorus (MBP), and acid phosphatase activity (APA) compared with the Chinese fir plantation. Also, soil phosphorus contents were shown as mature Chinese fir interplanting forest > young Chinese fir interplanting forest > young pure Chinese fir plantation. (2) The contents of active phosphorus fractions were the lowest and NaHCO₃-Po dominated within the active components. Soil NaOH-Po was the main component of moderately active phosphorus, especially in the mature Chinese fir interplanting forest. The content of Residual-P was the highest among total phosphorus. (3) The mature Chinese fir interplanting with broadleaves trees showed significantly increased contents of resin extracted phosphorus (Resin-Pi), sodium bicarbonate extracted organic and inorganic phosphorus (NaHCO₃-Pi, NaHCO₃-Po), sodium hydroxide extracted organic and inorganic phosphorus (NaOH-Pi, NaOH-Po), sodium hydroxide residual extracted organic phosphorus (NaOHu.s-Po), hydrochloric acid extracted phosphorus (HCl-Pi), and Residual-P. There were no significant differences in soil total inorganic phosphorus, NaHCO₃-Po, NaHCO₃-Pi, HCl-Pi, NaOHu.s-Pi, and Residual-P contents between young Chinese fir interplanting forest and pure Chinese fir plantation. (4) There were positive correlations between soil phosphorus fractions and soil physical and chemical properties (such as soil total carbon and nitrogen, dissolved organic nitrogen, microbial biomass phosphorus, acid phosphatase activity) for different interplanting forests except for soil water content (P<0.05). Redundancy analysis (RDA) indicated that the changes in phosphorus fractions were mainly driven by MBP. Moreover, soil organic phosphorus (NaOHu.s-Po, NaOH-Po) and HCI-Pi was positively correlated with MBP. In conclusion, soil phosphorus availability in Chinese fir interplanting forests were higher than that in young pure Chinese fir forest, and soil nutrient status were also better.