Abstract: The content of sodium ion in one steam generator blowdown system cannot satisfy the WANO chemical indices. This paper analyzes the possible causes of sodium ions in the secondary loop of the nuclear power plant and the difference of water quality indicators before and after the operation of the condensate polishing plant. It is concluded that the resin regeneration effect of the condensate polishing plant directly determines the sodium ion content in the steam generator sewage. With the ATE regeneration,  the removal of the oil contamination can be maximized and  the sodium hydroxide consumption during the regeneration of the anion resin of mixed bed can be reduced, and the sodium ion content in the steam generator sewage can satisfy the WANO chemical indices when the ATE is operating.