Abstract: Detailed physicaland chemical characteristic analysis wasperformed on the spent cation and anion resins in the mixed bed from Xi’an Pulse Reactor water purifying system. The exchange performance variations of used resins and the contributions from different factors to the variation were discussed. Based on the obtained information of the impurities in the used resin, the contamination state of the water in the Xi’an Pulse Reactorwater pool, the corrosion state of the structural material in the reactor was presented. The spent anion resin almost completely losses its exchange performance, while the remaining exchange capacity in the spent cation resin is still high. The radiation field from the reactor operation contributeslittle to the degradation of the performance of the resins. The exchange capacity loss of the spent anion resin is due to the exchange of its active groups into abundant carbonate and a certaint amount of organics. The impurityamount in the anion and cation exchange resins islow, which suggests that the water in the Xi’an Pulse Reactorwater pool is little contaminated. A certain extent of corrosion is occurred on the structural material in the swimming pool of the reactor. The results provideimportant referential data for the operational safety of the water purifying system of similar research reactor.