Abstract: An ion chromatographic method with the automatic sample pretreatment (on-line pre-concentration) technique combined with ultra-large volume sample injection (10 mL) for the determination of trace anions (ng/L level) in ultra pure waters from power plants was established. The high capacity hydroxide-selectivity IonPac AS18 anion exchange column, Eluent Generator (EG) which automatically and on-line produce gradient KOH eluent, and suppressed conductivity detector were used for the separation and detection of anions. A new on-line water purification technique and equipment, CIRA device, was introduced to ion chromatographic system, which on-line purified the "waste solution" from conductance cell. The purified high grade de-ionized water flushed the sample from large loop in ten-port valve to the low pressure concentrator in six-port valve and then the sample injections were achieved through the valve-switching technique. The new method coupled with CIRA technique can provide the advantages of stable system blank, high automation, easy operation, excellent reproducibility, high sensitivity, good stability, time saving and low cost. The detection limits of the method for anions are lower than 2 ng/L with linear coefficient of higher than 0.999 and precision of 1.151% RSD to 3.347% RSD (n=10). The method has been applied to the determination of trace anions in ultrapure waters from power plants and nuclear power plants.