In this work, the kinetics of the polyvinyl butyral (PVB) synthesis reaction catalyzed by the deep eutectic solvents (DESs) at the low‐temperature stage was studied to control the particle size of PVB resin and optimize its synthesis process. The effects of stirring speed, the concentration of polyvinyl alcohol (PVA), catalyst dosage, and temperature on the synthesis reaction of PVB were investigated. The data obtained from kinetic experiments at 283.15–298.15 K were fitted with the shrinking core models, and the results showed that the model controlled by internal diffusion fitted well with the experimental data. The internal diffusion coefficient, DA, of n‐butanal in the product layer was further calculated by the obtained model parameters, and it was applied to predict the synthesis reaction of PVB at different concentrations of n‐butanal. The results indicated that the shrinking core model controlled by internal diffusion is suitable to describe the kinetics of the PVB synthesis reaction. DES played a dual role in catalysis and dispersion in the synthesis of PVB, and it was a green catalyst with good potential for PVB industrial applications.