Karst desertification areas are extremely fragile ecological environments. The migration and transformation of Polycyclic aromatic hydrocarbons (PAHs) in desertification soils are still rarely studied, and the relevant impact mechanisms remain unclear. The study selected lime soil with different rocky desertification grades in southwestern karst area and phenanthrene and pyrene in the environment as the research objects, and investigated the desorption behavior of PAHs in different rocky desertification soils and the impact mechanism of earthworm bioavailability. The results showed that in severe rocky desertification soil (SRDS), moderate rocky desertification soil (MRDS) and light rocky desertification soil (LRDS), fraction of rapid desorption (F_rap) of phenanthrene increased by 18.51%, 14.03% and 9.65%, respectively compared with non-rocky desertification soil (NRDS); F_rap of pyrene increases by 15.79%, 5.53% and 4.32%, respectively. The bioavailability fraction (F_bio) of PAHs in karst desertification areas was about twice that of Tenax1-6h extraction concentration. The desorption intensity and bioavailability components of PAHs in soils increase with the increase of rocky desertification. Pearson and redundancy analysis（RDA）showed base saturation, porosity and SOC were the main physical and chemical properties that affect the desorption capacity and bioavailability accumulation factors of PAHs in karst soils. Calcium ions in the soil of karst desertification areas may promote the desorption of PAHs.