The reaction mechanism of glyoxal(G)with urea(U)under weak acid condition was theoretically investigated at PW91/DNP/COSMO of quantum chemistry using density functional theory(DFT)method.The results show that the addition reaction of G with U under the conditions mainly involves the reactions of U with protonated glyoxal(p-G),protonated 2,2-dihydroxyacetaldehyde(p-G1)and protonated bis-hemdiol(p-G2)to form two important carbocation reactive intermediates of C-p-UG and C-p-UG1,and two important hydroxyl compounds of UG and UG1.These compounds play important roles in the formation of UG resin.According to the result of quantum chemical calculation,UG resin was synthesized successfully under weak acid conditions.The UG resin was characterized by matrix assisted laser desorption ionization time of flight mass spectrometry(MALDI-TOF-MS),ultraviolet and visible spectroscopy(UV-vis),Fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resonance spectroscopy(13CNMR and1HNMR).These instrumental analytical results agree with each other and further confirm the addition reaction pathway of glyoxal with urea proposed by quantum chemical calculation. The reaction mechanism of glyoxal (G) with urea (U) under weak acid condition was theoretically investigated at PW91 / DNP / COSMO of quantum chemistry using density functional theory (DFT) method. The results show that the addition reaction of G with U under the conditions mainly involves the reactions of U with protonated glyoxal (pG), protonated 2,2-dihydroxyacetaldehyde (p-G1) and protonated bis-hemdiol (p-G2) to form two important carbocation reactive intermediates of Cp-UG and Cp- UG1, and two important hydroxyl compounds of UG and UG1. These compounds play important roles in the formation of UG resin. According to the result of quantum chemical calculation, UG resin was synthesized successfully under weak acid conditions. The UG resin was characterized by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS), ultraviolet and visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (13CNMR and 1H NMR) instrumental analytical results agree with each other and further confirm the addition reaction pathway of glyoxal with urea proposed by quantum chemical calculation.