Fluorescence analysis is an important technology, which can obtain the concentration of target analytes through comparing the fluorescence intensity change of a fluorescent sensor. Generally, the fluorescence intensity is measured by a fluorometer. However, many undergraduates have no chance to operate such an expensive instrument. Besides, the students cannot see the fluorescence of the obscured samples during the fluorometer-based detection process. Herein, a flexible experiment for fluorescence analysis was designed using a smartphone for recording fluorescence photographs and the software, Photoshop or ImageJ, for measuring the fluorescence intensity. The change in fluorescence intensity can be directly observed by naked eyes and be quantitatively measured by Photoshop or ImageJ. RhBN, with a simple synthetic process, was chosen as a ClO[superscript -] sensor, whose fluorescence emission significantly increased in the presence of ClO[superscript -] because of the strongly enlarged conjugated system. The experimental course designed in this article overcame the requirement of an expensive fluorometer and provided an interesting and simple approach for educating undergraduates about fluorescence analysis and fluorescent sensors.