Triethanolamine (TEA) was used to modify solvent-free reactive layer of polyaryl polymethylene isocyanate (PAPI) and polyester polyol system for obtaining coated urea. The crosslink density, crystallization morphology, thermal stability and molecular structure of the films were characterized by the swelling method, differential scanning calorimetry (DSC), thermal gravimetric analysis (TG/DTG) and attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR), respectively. And the effect of the mass fraction of TEA on controlled-release property of coated urea was investigated. The results showed that the crosslink density and glass transition temperature of the film increased with the increase in mass fraction of TEA. The degree of hydrogen bonding of carbonyl groups in the film was reduced after TEA was added, but the CH2 bending vibration absorption was enhanced. When the mass fraction of TEA was 2.6%，the control release duration of coated urea was extended by at least 25 d, compared with coated urea without modification treatment.