Soil polycyclic aromatic hydrocarbons (PAHs) pollution has seriously threatened human life and health and the safety of the ecological environment. The effects of initial PAHs concentration, soil moisture and particle size on the desorption efficiency were investigated by ex-situ thermal desorption experiments, and the primary and secondary kinetic and exponential decay models were used to fit the thermal desorption to explore the removal mechanism of PAHs' thermal desorption in soil. The results showed that the desorption efficiency increased with higher initial PAHs concentration under the same conditions. When the desorption lasted 20-40 min, a significant efficiency improvement was observed. The effects of soil moisture varied with different PAHs components:Nap, Phe and Ant reached optimal removal rate when the moisture was 16%, while the maximum removal rate of Fla and Pyr occurred with 13% moisture. Under the same desorption conditions, the smaller the soil particle size, the higher the removal rate of PAHs in the soil. The results showed that the exponential decay model has a better fitting effect on the desorption process of PAHs components. PAHs' thermal desorption is divided into two main stages:1) PAHs evaporate from soil particle surface with water evaporation; 2) the diffusion within soil pores restricts PAHs' evaporation rate.