Abstract: The experiment was conducted to study the histopathological changes of piglets infected by PRRSV-FJ04A and its distribution in the infected piglets. PRRSV-FJ04A strain was used to infect the 30-day-old healthy piglets. The pathological changes and distribution of virus in the organs including airtube, digestive canal, urinary tract, immune organs were analyzed by histopathology observation and real-time RT-PCR assay. The results showed that the piglets were killed 10 days after infected，that there were a lot of metamorphic and necrotic alveolar cells, hyperplastic macrophages in the lung. It also caused necrotic lymphocyte of lymphaden and neuron degeneration even neorobiosis of brain. And a lot of cell debris in acinus lienalis, granular degeneration of liver and exuviation of cryptae tonsillares were found. There were a large amount of virus in the lung, followed by lymph gland, brain, amygdala and blood. And kidney was found to have the least virus.