Abstract: This paper deals with affection to tissues and cells of Paulownia which is infected by MLO.By means of electron microscopy ,it is found that a large amount of callose accumulate in the infected cells and fill in sive mesh and path between cells. By means of atomic absorption spectrometry,the rate of electrolytic out-seeping was measured,the result shows that the rate of electrolytic out-seeping in the healthy xylem is 59.17%, but in the infected xylem is 8.82 %, the rate of electrolytic out seeping in the healthy cortex is 2.26%,but in the infected cortex is 21.81%.By means of microscopy,the tissues structure of branchs was measured,the result shows that the cambium relativity thickness in the healthy branch is 10.28 μm, but in the infected branch is 6.71 μm,cortex and xylem relativity thickness are unchanged basically.