Phosphorus sorption and desorption characteristics of gray desert soil (0~20 cm) under long-term fertilization as affected by phosphorus content level were studied through an isothermal P adsorption and desorption experiment. Results show that within the range of P concentrations set for the experiment, in all the gray desert soil samples, regardless of Olsen-P level, P adsorption, P desorption and P desorption rate gradually increased and P adsorption rate gradually decreased, with the increasing amount of extraneous phosphorus added. A positive correlation was observed between Olsen-P content and phosphorus sorption saturation ( DPS) in the soil. In terms of soil maximum adsorption capacity ( Xm), the treatments of the experiment followed a decreasing order of CK > NPK ≈ NPKM > PK ≈ NPKS, and the differences between the treatments were extremely significant; Treatment NPK was much higher than CK and Treatments PK, NPKM and NPKS in adsorption constant (K) and maximum buffer capacity (MBC). And the comparison between last four treatments showed no significant difference in K value, and CK was extremely higher than Treatments PK and NPKS in MBC value, but the difference between CK and Treatment NPKM, and between Treatments PK and NPKS was not significant. Treatments NPKM and NPKS were significantly higher than Treatments NK and NPK in RDP, and Treatment NPKM was the highest in P desorption rate.