The invention provides a detecting device and method for detecting flow injection chemiluminescence water inorganic mercury, aims to solve the problems that in the prior art, an ozone solution is easy to decompose, on-site operation cannot be performed, analyzing time is long, analyzing process is complicated, conditions are rigorous, energy consumption is high, secondary pollution can be produced and the like. A catalyst of ruthenium trichloride is filled into a dynamic ozone solution balancing pipe; when the ozone solution flows into the dynamic ozone solution balancing pipe, the catalyst of the ruthenium trichloride is irradiated by a fluorescent light, the ozone in the ozone solution is inhibited from generating hydroxyl radicals, the ozone solution is stable and decompose rarely, and stability of the ozone solution is improved. The detecting device used for detecting the inorganic mercury in water has the advantages of scene, rapidness, convenience and flexibility.