In this work, a tetraphenyl ethylene functionalized rhodamine chemodosimeter, namely, TRP, has been designed, built, and structurally determined. The chemodosimeter exhibited an AIE effect in an EtOH-H2O mixture with the maximal emission intensity at 463 nm at a water fraction of 70 %. Then TRP was applied for ratiometric monitoring of Hg2+ ions in EtOH/H2O solution (v/v = 3/7), presenting about a 35-fold fluorescence intensity ratio enhancement (F649/F463), visible color changes, and well-resolved emission bands (187 nm). In addition, TRP showed high selectivity and sensitivity in Hg2+ ions sensing and achieved a limit of detection (LOD) of 10.0 nM, which was mainly attributed to the production of an oxadiazole functionalized and spirolactam ring opened rhodamine derivative-induced by Hg2+ ions. Significantly, using TRP as a tracer, ratiometric fluorescent detection of Hg2+ ion has been successfully conducted via living cell imaging, demonstrating its potential for practical applications in biological systems.