Surface photovoltage inversion was found in PbI2 microcrystals, manifested as a significant increase in the absolute value of surface barrier height under sub-bandgap illumination. The corresponding surface states located at 0.43 eV above the valence band was detected, and the magnitude of photovoltage inversion was found to increase with increasing applied field strength. Besides, transient surface photovoltage responses and the time constants of the relaxation showed a dependence on the wavelength of illumination. When irradiated with 518-632 nm, the exciton together with the lead ion vacancy caused the population of holes in the surface state; while under 700-nm light irradiation, holes depopulation occurred on the surface. Transient surface photovoltage results show that the relaxation of the sub-bandgap surface photovoltage is exponential with long time constant. The different charge transportation processes agree well with the photocatalytic degradation of MO experiments under different wavelength irradiation. It is revealed that the exciton and the surface states could significantly affect the movement of photogenerated charge carriers, which lead to different degradation results of MO. These findings demonstrate a model involving photostimulated population of surface states for the study of surfaces of wide energy gap semiconductors, which shows the highly selective control of photogenerated charge carriers' behaviors by tuning the wavelength of irradiation.