Abstract: To clarify the occurrence, molecular evolution and system conduction characteristics of potato virus Y, which causes vein necrosis and mosaic leaves in Qingdao experimental field.The prevalence of virus disease in Qingdao experimental field was determined by viral disease phenotype, incidence rate and disease index;MEGA7 was used as a phylogenetic tree to identify the strains of PVY Qingdao isolate;qRT-PCR, western blotting and PVY-GFP were used to clarify the conduction path of PVY-infected plants;diseased leaves were sampled from different leaf positions and disease symptoms, and the relative content of CP mRNA was used to clarify the viral content of leaves with obvious symptoms and latent symptoms;the CP content of the three viruses when TMV, CMV, and PVY infected alone, mixed with the two, and mixed with the three were detected to clarify the interference or synergistic effects of the viruses mixed infection.The results showed that PVY mixed seriously with TMV and CMV infection in the maturity stage, and the PVY isolate was an N:O strain, which did not break through the resistance of the va gene.In the early stage of infection, the virus enters the stem from the inoculated leaf along the veins, and when it begins to transport in two directions, it first moves to the root, and then reaches the seedling tip;then spreads to the upper leaves, and then slowly moves to the lower leaves;finally, it continues to transport to the new parts at both ends as the tobacco plant grows.The recessive symptoms of the upper leaves were obvious in the mid-infection stage, and the symptoms of diseased leaves were positively correlated with the virus concentration.In the middle and late stages of the tobacco field, PVY is mixed with TMV and CMV, and the interference and synergy between viruses lead to complex and changeable symptoms.The research results will help improve the accuracy of the variety resistance identification test and the target of the drug efficacy test.