To investigate the changes of hematological traits after infection with highly pathogenic porcine reproductive and respiratory syndrome virus, a total of 72 Large White×Tongcheng advanced generation inter-cross piglets of 5 weeks old ,infected with HP-PRRSV, were used for the artificial infected experiment. The WBC count, the lymphocyte percentage, the monocyte count and the granulocyte percentage were determined at 0,4,7,11,14,21,28,35 days post infection (DPI) ,then were correlated with viremia respectively. The results showed when compared to 0DPI, the WBC count, the lymphocyte percentage and the monocyte count were significantly reduced (P <0.01), and the granulocyte percentage was significantly increased (P <0.01) at both 4DPI and 7DPI, but there were no significant differences for the other DPI. Groups of piglets with PRRS-resistant and PRRS-susceptible were set on the basis of viremia and survive. It was detected that the lymphocyte and the granulocyte percentage were significantly different at 7DPI between groups. The lymphocyte percentage was significantly higher than PRRS-susceptible group(P <0.05), and the granulocyte percentage was significantly lower (P <0.05).For other DPI, as well as other hematological traits, there were no significant differences. Furthermore, the correlation analysis of hematological traits and viremia at all DPI in piglets revealed medium correlations between the hematological traits and viremia (P <0.01). Our current study provides basic data for further research on the changes of hematological traits after PRRSV infection and its relationship with viremia deeply.