The highly pathogenic porcine reproductive and respiratory syndrome (PRRS) is the most important infectious disease of pigs. The host would respond to PRRSV by regulating different immune responses at different days post infection (DPI). The routine blood testing is the most intuitive way to detect changes of blood cell in the body. Therefore,it is necessary to detect and analyze hematological parameters for predicting the process of the disease. To investigate the changes of hematological parameters after infection with HR-PRRSV,72 Large White×Tongcheng advanced generation inter-cross piglets with an average age of 11 weeks,were used for the artificial HP-PRRSV infection experiment. The white blood cell (WBC) count,the lymphocyte percentage,the monocyte count and the granulocyte percentage were determined at 0,4,7,11,14,21,28,35 DPI,then association analysis of them with viremia were carried on. The results showed that when compared to 0 DPI,the WBC count,lymphocyte percentage and monocyte count were significantly reduced,and the granulocyte percentage was significantly increased at both 4 DPI and 7 DPI. The lymphocyte percentage was significantly reduced and the granulocyte percentage was significantly increased at both 11 DPI and 14 DPI,but there were no significant differences at the other DPI. Groups of piglets with PRRS-resistant and PRRS-susceptible were set on the basis of viremia and survive rate. It was showed that the lymphocyte and the granulocyte percentage were significantly different at 7 DPI between groups. The lymphocyte percentage of the PRRS-resistant group was significantly higher (P<0.05),and the granulocyte percentage was significantly lower (P<0.05) than the PRRS-susceptible group. For other DPI,as well as other hematological parameters,there were no significant differences. Furthermore,correlation analysis showed that the hematological parameters and viremia at all DPI in piglets were moderately correlated (P<0.01). The results demonstrated that the lymphocyte percentage and granulocyte percentage could be used as indicators of resistance to PRRS. Our current study provides basic data for further research on the changes of hematological parameters after PRRSV infection and relationship with viremia.