Abstract: The histological structure of Tylorrhynchus heterochaetus was systemically observed. According to histological staining, there were strong muscles (circular muscles and longitudinal muscles) in the body wall of T.heterochaetus. The heads epiderm contained many mucous glands (pyriform gland and tubuliform gland) and sensory cells, whose function was to excrete mucus and to helphead judge direction. There was a parapodia on each metamere of the worm, inserted with several setae and surrounded by abundant capillaries. The pharyngeal muscle in the pharynx of digestive tract was strong, with a short esophagus and an obscure stomach. The intestinal tract was divided into two parts (foregut and hindgut): the foregut was thicker than the hindgut and consisted of much elevation, which was suitable for milling food, while the hindgut was much thinner but had abundant glands clustered in its inner surface, being important for digesting food and absorbing nutrition. The circulatory system was a typical closed vascular one, containing a big dorsal vessel, a big ventral vessel, a vascular sinus and some small protovertebral vessels. The nervous system consisted of a pair of suprapharygeal ganglions and a ventral nerve cord.