Microplastics (MPs) and neonicotinoid pesticides are widespread pollutants in agricultural soils, but their interactions have not been fully studied. This study focuses on the interactions between biodegradable MPs, poly (butylene succinate) (PBS), and the neonicotinoid pesticide thiacloprid (THI). The experimental results show that the adsorption process of PBS on THI is more consistent with the pseudo-second-order kinetic model, indicating that chemical adsorption is predominant. Adsorption isotherm analysis indicates that the adsorption of THI by PBS is multi-layered, and both the Henry model and the Freundlich model fit the adsorption data well (R2 > 0.99), while the Langmuir model fits poorly. The study on the influence of environmental factors on adsorption has found that an increase in pH and salinity promotes the adsorption of THI, while the concentration of dissolved organic matter has little effect on adsorption. Desorption experiments found that in simulated intestinal fluid (SIF), the maximum desorption amount of THI by PBS is 39.4 μg g_^-1, which is 1.157 times that in pure water, indicating that THI is more easily desorbed in the SIF environment. The application of Diffusive Gradients in Thin-films (DGT) technology revealed that the bioavailability of THI in soil increased after the addition of PBS, and further increased with the increase of PBS addition ratio. These findings provide important information for understanding the impact of MPs on the environmental behavior of neonicotinoid pesticides under actual environmental conditions and offer a new perspective for the environmental risk assessment and management of pesticides.