Abstract: In this study, humic substance fractions were extracted from Brown coniferous forest soil, Dark Brown soil, and Yellow Brown soil. Humic acid (HA) was separated by acidification using a conventional method of alkali (0.1 mol L⁻¹ NaOH + 0.1 mol L⁻¹ Na₄P₂O₇) extraction procedure. Alkali-insoluble crude humin (CHU) was treated with 10% HF-HCl to obtain pure humin (PHU) through removal of mineral ash. The availability of humic substance fractions-bound phosphorus (P) was analyzed using the methods of enzymatic hydrolysis and ultraviolet irradiation. The results showed that the content of P in the tested humic substance components was the highest in HA, followed by PHU, and the lowest in CHU. About 32.1%-51.7%, 17.2%-28.5% and 22.3%-35.7% of HA, CHU and PHU -bound P were in the form of labile inorganic P, while 29.5%-37.6%, 20.6%-31.1% and 26.2 %-41.5% of them was in the form of labile organic P. In the labile organic P, phytate-like P displayed the highest proportion (9.51%-27.6%), followed by simple monoester P (5.89%-13.7%), and the proportion of polynucleotide P (1.03%-9.28%) was the lowest. Compared with samples without UV irradiation, UV irradiation combined with enzymatic hydrolysis increased the proportion of labile P in the HA, CHU, and PHU fractions by 0.90%-3.77%, 0.73%-7.57%, and 0.69%-3.91%, respectively. The content of total labile P in the humic substance components decreased in the order of HA > PHU > CHU, while the opposite order was found in the content of recalcitrant P. Total labile P was significantly negatively correlated with Al content, while recalcitrant P was significantly positively correlated with Al content. The availability of HA-bound P was the highest, followed by that of PHU-bound P, and that of CHU-bound P was the lowest. The existence of Al can inhibit the availability of humic substance -bound P.