The invention provides a ruthenium (II) complex, a ruthenium (II) complex-TiO2 functional film and application of the ruthenium (II) complex-TiO2 functional film, belonging to the technical field of rapid detection of Hg<2+>. The ruthenium (II) complex-TiO2 functional film comprises Ru(ptbpyH)2(SCN)2, TiO2 nano-particles and an FTO electrode. Under the stimulation of visible light, the functional film is capable of conveying photoelectrons to a photoelectrode and generating an initial light current. Hg<2+> is added into a reaction solution and generates a coordination effect with isothiocyanate radical, so that the level structure of a complex is changed, and the light current is rapidly decreased; and color comparimetry/photoelectricity double-mode detection of Hg<2+> can be realized by virtue of the functional film according to the change of the light current and color before and after the reaction between a sensing interface and Hg<2+>, and the functional film has the advantages of high sensitivity, good selectivity, high analysis speed, good repeatability, low cost, small equipment, easiness in microminiaturization and the like.