At present, the rapid evaluation methods of urea formaldehyde fertilizer (UFF) efficiency are based on the activity coefficient method of urea formaldehyde (UF) water solubility, but the specific operating rules and technical indexes are different in different countries and regions because of activity coefficient method limitation. The nutrient release rate of UFF is directly related to the structure of UF, which is not directly related to its solubility in aqueous solution at different temperatures. Therefore, it is more reasonable to study the nutrient release from UF structure. In this study, we investigated the feasibility of fourier transform infrared spectroscopy (FTIR) to evaluate the structure of UF under different factors of water content, urea content and formaldehyde storage time, so as to find a new UFF evaluation method. We investigated the relationship between the infrared absorption spectra of the product under different reaction conditions, the amount of product produced and the nutrient release of the reaction product of different urea in the acidic environment. It can be seen from the research results that the spectrum can reflect the change of water and urea addition and the change of formaldehyde storage time on the relative strength of the absorption peak of the characteristic group of UF. Through these changes, the change of UF composition can be judged. These judgments can be confirmed from the amount of the product, and the results of the soil culture experiments were further confirmed by the infrared spectrum to determine the correctness. The above results showed that it was feasible to study the fine change of UF structure by infrared absorption spectroscopy. If the mathematical model was established between the fine changes of urea formaldehyde infrared spectrum and UF nutrient release in the soil, a new means to assessment UFF fertilizer efficiency would be provided accurately and rapidly.