The wavelength dependence of the electron localization in dissociating molecular ion D2+ is investigated via solving the time-dependent Schrödinger equation of the two-state model of the molecular ion. Our results reveal an anomalous dependence of the electron localization on the laser wavelength. Overall, the degree of the electron localization shows a growing trend with the increase of wavelength, but it drops off obviously at some wavelengths. It is found that the localization asymmetries for some vibrational states become opposite in phase when the wavelength is changed, leading to the decline of the electron localization. Further analysis shows that the nuclear and electronic motions that determine the electron localization respond inconsistently to the variation of the wavelength, ultimately resulting in the non-linear dependence of the electron localization on the laser wavelength.