Microplastics (MPs) and perfluorooctanoic acid (PFOA) are ubiquitously present in agroecosystems, which can cause varying degrees of environmental damage. This study reports the investigation of the effect of MPs on PFOA adsorption by soil. A comprehensive analysis was performed on the adsorption–desorption dynamics of PFOA by MPs and soil under different conditions. The surface morphology of MPs and their interaction with PFOA were characterized. Irregularly shaped MPs facilitated accurate simulation of real-world conditions, influencing the adsorption quantity of PFOA in soil. Additionally, the peak intensity of various preadsorption and post-adsorption MP functional groups was altered, indicating that MPs augmented PFOA adsorption. The kinetics of PFOA adsorption followed the quasi-second-order reaction, and the isotherm data aligned well with the Freundlich model. This study reveals the mechanism by which the co-sorption of PFOA and MPs in agroecosystems affects their respective environmental behaviors, providing basic research data for the control of pollutants in agroecosystem soil.