Graphite carbon nitride (g-C3N4) has become the hot research material in the field of photocatalysis. In this study, Er-doped g-C3N4 was synthesized by methanol-refluxing method using melamine as precursor. The resulting composite photocatalysts were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ultraviolet-visible-near infrared reflection spectrophotometer (UV-Vis-NIR Spectrophotometer), infrared spectrum (IR), photoluminescence spectroscopy (PL), N2-physisorption and confocal laser scanning microscopy (CLMS). Results indicate that the rare-earth metal Er is highly disperse on g-C3N4 and it is favor for the introduction of nitrogen vacancies. The addition of Er optimize the energy band structure of g-C3N4, enhance the absorption of visible light, improve the electron-hole separation rate, furthermore, it is also found that Er/g-C3N4 photocatalyst process strong upconversion ability. The photocatalytic degradation of rhodamine B solution is performed under 660 nm LED red-light irradiation, and the rate constant of the Er/g-C3N4 is 2.0 times as high as that of pure g-C3N4. It is also found that the superoxide radical is the main active species for catalytic reaction in this system.