Coated fertilizer is a hot spot in the domain of fertilizer research. Related researches mainly focused on the action mechanisms of coating materials in controlling the nutrient release from coated fertilizers, but less information is available on the structural variation of the coating materials before and after spraying on fertilizers, which is the key to whether we can directly use coating materials to extrapolate its mechanisms in controlling coated fertilizers’ nutrient release. With polylactic acid (PLA), poly (butynelenes succinate) (PBS), and polycarbonate (PC) as test materials, the variations of their IR spectra before and after spraying on urea fertilizer were determined, which was aimed to supply theoretical basis for further studying the action mechanisms of coating materials in controlling coated fertilizers' nutrient release. The results showed that PLA and PC had less variation in their IR spectra before and after spraying on urea fertilizer, while PBS acted in reverse, suggesting that the former two coating materials could be directly used for studying the patterns of nutrient release from coated fertilizers.