Abstract: Introduced a method of probing brittle fracture mechanism of damaged PVC slice.The fractured PVC slice (A) is contrasted with unfractured PVC slice (B) in compositon,crystallinity,soft point,mechanical properties and surface form by FT-IR,X-ray fluorometer,XRD,thermal analysis instrument,tensile test bed and SEM.The research showed that ① Both of A and B consist of PVC resin, plastifier and a little additive. The plastifier quantity of A is 10.42%.The plastifier quantity of B is 15.5%.② The crystallinity of A is 13.3%.The soft point of A is 64.2℃;The crystallinity of B is 5.6%.The soft point of B is 56.5℃.③ Wearing state structure of A is elevation orientation.There are cracks less than 1μm.Their directions are parallel to the slice orientation.Vertical tensil strength of A is 55.38MPa.Horizontal tensil strength of A is 41.6MPa.④ Wearing state structure of B is "woolen blanket".The vertical tensil strength of B is 67.24MPa.The horizontal tensil strength of B is 64.25MPa. In this paper,we have a discussion on the fractured mechanism of PVC slice.The fracture of PVC slice is caused by bad plastication and the elevation orientation of these slices.The elevatio orientation of these slices is caused by one way tension.