7-hydroxyquinoline (7-HQ) is a kind of organic molecule with excited-state proton transfer (ESPT) effect. 7-HQ in ethanol solution causes ESPT reaction under the excitation of ultraviolet light. The fluorescence spectrum of the sample exhibits two bands. In contrast, 7-HQ in dimethyl sulfoxide (DMS) solution does not cause ESPT reaction. The fluorescence spectrum of the sample exhibits a single band. But after the sample was irradiated with a strong UV light, its fluorescence spectrum also exhibits two bands. This phenomenon is reported for the first time in the present paper, and its cause is investigated through the study on the absorption spectra and fluorescence spectra of 7-HQ in ethanol, dimethyl sulfoxide and N, N-dimethyl formamide solution. The conclusion is that the change in the fluorescence spectrum of 7-HQ in DMS solution is due to the fact that 7-HQ causes ESPT reaction which results from the photodecomposition of DMS and the product of water after the solution was irradiated with strong UV light.