The structure and deformation eharacteristics of PS film craze in pregnant．gro-wth．mature and failure process were studied by transmission electron microcopy (TEM)．It is presumed that the fine white lines extended from craze tip along craze propagation direction are resulted from the tearing of PS molecular chain under ten-sile stress field．According to Our experimental results．the authours proposed the cold-drawn mechanism and transverse constraction of craze matter during plastic de-formation．It was observed that the primary craze matter broke in accordance with the“tearing cloth” model and the crack．tip crazes have shape described by the DugdMe model．It was discoverd by TEM that the craze thickness increased in two ways．by the elongation of primary craze matter and by the converting of PS moleculers on craze／matrix polymer interface into craze，proposed by E．J．Kramer．