Abstract: A new variety with genetic improvement of K326 (Y48) has great market potential. Y48 was developed by marker-assisted selection for its high anti-TMV & CMV ability with the same agronomic traits. In order to reveal the cytological mechanism of the Y48 resistance, transmission electronic microscopy (TEM) was use to observe the ultrastructure of K326 and Y48 leaves in 0-72 h after TMV inoculation. The results showed that, in K326, chloroplast thylakoid lamellae decreased, mitochondria crista expanded, and autophagy appeared in mesophyll cells at 24 h after TMV inoculation. The chloroplasts and mitochondria were completely destroyed by TMV, then mesophyll cells went through pathological necrosis at 72 h after inoculation. While in Y48, a small amount of particles were deposited inside the chloroplast, the mitochondria cristae degraded, and the degraded-like vesicles appeared in mesophyll cells at 48 h after TMV inoculation. Chloroplasts and mitochondria were degraded totally, cytoplasm was concentrated, mesophyll cells went through programmed cell death (PCD) at 72 h after inoculation. The results indicated that, compared to K326, Y48 could delay TMV infection and activate hypersensitivity response to lead mesophyll cell to go through HR-PCD. Add, the present of peroxisome in Y48 at 72 h agter inoculation, might effect ROS level of cell. The two differences might provide cytological evidence to reveal the Y48 resistance and give the clue to analyze the molecular resistance mechanism of Y48.