In this work, a highly branched polyurea (HBP-NH₂) similar to urea structure was introduced to phenol-formaldehyde (PF) resin to accelerate itscuring speed The results of gel time and bonding strength were combined to obtain a good modified additional stage and amount of HBP-NH₂. The relative molar mass changes of HBP-NH₂-modified PF resin were investigated by gel permeation chromatography (GPC). The effects of HBP-NH₂ on the curing of PF resin were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The effect of HBP-NH₂ on the structure of PF resin was also investigated by nuclear magnetic resonance carbon spectroscopy (¹³C-NMR). The test results show that the gel time of the modified PF resin was reduced by 32% and 51% at 110 °C and 130 °C, respectively. Meanwhile, the addition of HBP-NH₂ increased the relative molar mass of PF resin. The bonding strength test showed that the bonding strength of modified PF resin increased by 22% after soaking in boiling water (93 °C ± 2) for 3 h. The DSC and DMA analysis indicated that the curing peak temperature decreased from 137 °C to 102 °C, and the curing rate of the modified PF resin was also faster than that of the pure PF resin. The ¹³C-NMR results showed that HBP-NH₂ in the PF resin reacted to produce a co-condensation structure. Finally, the possible reaction mechanism of HBP-NH₂ for the modification of PF resin was given.