Infrared absorption spectra of congruent lithium niobate crystals are measured at low temperature, and a new peak is found at 3200 cm-1 in the spectra. Results show that this peak has no relationship with hydrogen in the crystals, and that with the increase of the temperature, both the intensity and shape of the peak change in a complex way. Based on these results, we suggest that the new peak results from the electron transfer from small polarons （Nb4+Li） to free polarons （Nb5+Nb）. In addition, we find that this peak can be decomposed into three Gauss peaks, and the three components are attributed to three transfer processes with different energies.