The thermal behavior of pre-curing urea-formaldehyde (UF) resin with different solid content was investigated by different scanning calorimetry (DSC), and the activation energies (E-a) in different pre-curing stage of UF resin were also analyzed by Kissinger method. The results indicated that with pre-curing degree increasing, the DSC curves of pre-curing UF resin shifted to lower temperature, and both the onset and peak temperature decreased. The pre-curing process of UF resin included two stages: In the first stage, the E-a and Z value decreased obviously due to the activity of component increased with water evaporation, and then, these two values increased in the second stage due to pre-curing degree increased even partial resin was cured.