Abstract: The organs with cancers in CT image deform seriously and the traditional segmentation methods cannot segment the entire chest correctly.This paper presents a 3D mesh based segmentation method.Firstly,an initial chest skeleton is found using ribs and back bones; secondly a sphere triangle mesh is constructed and the correspondence between the mesh and the chest skeleton is created; thirdly the mesh is deformed according to three objective functions; finally the mesh is refined by edge voxels near the mesh and the segmentation result is refined.Experimental results show that the proposed method can efficiently segment the seriously-deformed chest in CT image,which is robust against the noise and deformation of organs.