Abstract: Abstract: Photosynthesis characteristics of flue-cured tobacco infected with tobacco mosaic virus (TMV) were studied. The results showed that the contents of chlorophyll and carotenoid decreased after TMV infection. The chlorophyll fluorescence parameters: Fv/ F0, Fv/ Fm, ? PSⅡ, qp and NPQ values all were reduced, while net photosynthetic rate (Pn) decreased. Stomatal limitation was the dominating factor of Pn reduction under slightly infection condition, but the dominating factor was non- stomatal limitation under severely infection condition.