Abstract: In this paper, three kinds of tannins were used as modifiers. The influences of tannin variety, adding stages and adding amount on the performance of MUF resin were studied, and the optimal results were analyzed with the test methods of FTIR and 13CNMR. The results showed that add 7% bayberry tannin to modify the MUF resin during the first alkali stage had the best results. The resin has an appropriate viscosity and low free formaldehyde content. The performances of glulam that made by the modified MUF resin satisfied the standardm on integrated structural timber in China. The results of FTIR showed that adding tannin would impede the reaction of additive reaction and polycondensation, enhance the stretching vibration of COC key in the modified resin, and weaken the stretching vibration of CN key. It agreed with the result of 13CNMR that the ether bond increased and the bridge bond decreased.