The detritus input and removal treatment is an experimental design to study the effects of aboveground litter and plant roots on soil nutrient cycling process and mechanism. In June 2012, we set up five treatments, viz. control (CT), no litter (NL), no roots (NR), no input (NI), and double litter (DL), in a natural evergreen broad-leaved forest of Castanopsis carlesii in Sanming, Fujian Province. Soil phosphorus fractions and their influencing factors in different soil layers (0-10 cm and 10-20 cm) of each treatment were studied in December 2018. The results showed that: (1) in the 0-10 cm soil layer, the total phosphorus content in DL treatment was significantly higher than that in NL treatment. The inorganic phosphorus content in NI treatment was the lowest, The organic phosphorus content in DL treatment was significantly higher than other treatments in 10-20 cm soil layer; (2) The contents of easily-available phosphorus fractions (Resin-P, NaHCO₃-Pi, NaHCO₃-Po) in DL treatment were significantly higher than those in other treatments in 0-10 cm soil layer. In 10-20 cm soil layer, the easily-available phosphorus and moderately-available phosphorus in NR treatment were significantly higher than those in NL treatment. The content of residual-P was the highest, but there was no significant difference between the treatment and soil layer; (3) The change trend of acid phosphatase in 0-10 cm soil layer was obvious among different treatments. CT treatment had the highest activity and NI treatment had the lowest activity. The difference between NR and NL treatments was not obvious in 10-20 cm soil layer. Redundancy analysis showed that the changes of soil phosphorus fractions were mainly affected by acid phosphatase, soil moisture content, dissolved organic nitrogen, and total nitrogen. Adding litter could mineralize organic phosphorus by increasing soil microbial biomass and enhancing soil acid phosphatase activity, promote the transformation of soil organic phosphorus to inorganic phosphorus, and improve the availability of soil phosphorus. However, root system could absorb soil active phosphorus and mineralize other phosphorus fractions. It had positive significance to improve the structure of P in soil.