To address the problems that the anti-disintegration property of surficial clayey soils is prone to deterioration under meteorological factors such as rainfall and drought, and traditional improvement materials such as cement and lime have defects such as high brittleness and irreversibility, the clayey soil in Nanjing area was taken as the research object to prepare improved soil samples with different lignin derivative contents and conduct disintegration tests. Combined with scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), the macroscopic and microscopic mechanisms of the anti-disintegration properties of clayey soils improved by lignin derivatives were revealed. The results show that the disintegration process of improved clayey soils is divided into three stages: initial saturation, rapid disintegration, and slow disintegration; the 1% content has the optimal effect, with the initial saturation stage extended to 9 min, the complete disintegration time doubled compared with that of untreated soil, and the average disintegration rate reduced by 20.13%; lignin derivatives form a film-like structure on particle surfaces to wrap and connect particles, reduce pore connectivity, introduce Ca2+ to enhance cementation, and inhibit water infiltration; when the lignin derivative content is too high, the films aggregate, interparticle connections weaken, and the anti-disintegration performance decreases.