A fast, precise, and accurate method that can simultaneously determine 7 anions in whole blood was established by on line dialysis-double suppression ion chromatography. Performance parameters which could affect the determination of anions were optimized, including the selection of protein precipitant in samples, the amount of filtrate discarded, selection of eluent flow rate, influence of the Ag-Na column on experimental results, influence of ethylenediamines on ClO2−, and investigation of nitrogen drying. Finally, 3.6 mmol/L sodium carbonate was selected as eluent, with a flow rate of 0.8 mL/min, to separate the 7 anions. Blood and alcohol (v/v, 1:4) were used to precipitate the proteins in blood. The 7 anions reached an adequate recovery rate when the first 2 mL of filtrate from the C18 column was discarded. The recovery rate at LLOQ, low, medium, and high concentrations was 80–120%. The correlation coefficients (r2) of the calibration curves of the targeted anions ranged from 0.9975 to 0.9998. The limit of detection (LOD) was 0.309–7.71 μg/L. This method has simple pretreatment, high accuracy, and good reproducibility and selectivity, and is suitable for the separation and determination of anions in blood.