Ultra high molecular weight polyethylene (UHMWPE) is a kind of non-polar polymer with a crystalline structure. Its failure appeared usually as a type of wire drawing when it was used as a material of rubbing pairs. By a designed heating test, the thermal damage phenomena of UHMWPE were observed by SEM. Its thermal damage model during the process of wire drawing damage was assumed that when the thermal energy was accepted by the UHMWPE, its volume expanding and its surface melting into a viscous fluid proceeded from its elevated temperature, and then the viscous fluid flowed according with non-Newtonian fluid model; after cooling, the melt re-crystallized and gathered again and at the same time many obvious cavities with phenomena of wire drawing appeared in the re- crystalline polymer. As a result the material of UHMWPE shrank to porosint from the congeries with the small uniform particles.