The invention discloses a rapid on-line diagnosis method for the deactivation condition of an SCR denitration catalyst, which comprises the following steps: tapping test holes on the wall surfaces of SCR denitration reactors above and below a catalyst bed layer to be tested; adding tracer gas above the catalyst bed layer through the test hole; monitoring the outflow position of the tracer gas below the catalyst bed layer to obtain the path of the tracer gas flowing through the catalyst bed layer so as to indirectly determine the flowing trace of smoke; simultaneously, measuring the NOx concentration, the O2 concentration, the smoke temperature and the smoke pressure at the tracer gas injection position above the catalyst bed layer and the corresponding tracer gas outflow position below the catalyst bed layer to work out the NOx removing rate so as to judge the deactivation condition of each area of the catalyst bed layer and further determining the positions of deactivated catalysts caused by blocking, poisoning and the like so as to provide beneficial references for the operation management and maintenance of the catalyst. The invention can carry out on-line monitoring on the deactivation conditions of the catalysts of SCR denitration devices, such as coal-fired boilers, gas fired-boilers, oil burning boilers, biomass-fired boilers and the like and has convenient operation and very good environmental protection benefit.