3-Methoxythioxanthone was synthesized, and the structure is identified by ¹H NMR, ¹³C NMR, IR and HRMS spectra. The UV-Vis absorption spectra of 3-Methoxythioxanthone shows that it absorbs near the purple light (380 nm) in the visible range and is a visible light photosensitizer. 3-Methoxythioxanthone was applied to the Aza-Henry reaction of 2-phenyl-1,2,3,4-Tetrahydroisoquinoline and Nitromethane. Under the irradiation of purple LED, the photosensitizer with a molar fraction of 5% allowed the reaction to be isolated in a yield of 84% within 6 h. According to the experimental results, the mechanism of photocatalytic reaction of AzaHenry was proposed. The photosensitizer could transfer energy to produce singlet oxygen under the illumination, and singlet oxygen promoted the Aza-Henry reaction.