Heat shrinkage behavior and characteristic change according to various drawing ratio are studied by testing polyethylene terephthalate film. The results are as follows: 1. Heat shrinkage behavior before necking state is corresponded to WLF formula and Arrhenius formula. 2. Heat shrinkage behavior of after necking state is corresponded to Arrhenius formula, but does not coincied with WLF formula. 3. In accordance with increasing draw ratio, transition temperature and density are decreased in before necking state, but those are increased in after necking state.