Dugesia japonica is usually used as model animal for the study of regeneration mechanism. In this study, an improved acetylcholinesterase histochemical method was used to locate the nerve system of D.japonica. The research results (DjAChE⁺) showed that the nerve system of D.japonica consisted of central nerve system and its branches, lateral nerve cords and peripheral epithelial nerve net. Dorsal and ventral nerve nets connected respectively with lateral nerve cords and formed the peripheral epithelial nerve net. Central nerve system was comprised of cerebral ganglion, ventral nerve cords and optic nerves. The multi-branch nerves from the central nerve connected with each other in the medial area of the cerebral ganglion and ventral nerve cords, which formed stomatic nerve ring in the medial mouth, which extended from pharynx root to pharynx tissue and formed pharyngal nerve net. The multi-branch nerves from the central nerve connected with both dorsal and ventral nerve nets, and then joined together with lateral nerve cords. The important findings in this research were that dorsal nerve net, ventral nerve net and lateral nerve cords coexisted in the D. japonica nerve system. This study provided the systematic neuroanatomical foundation for the regeneration mechanism of the D. japonica nerve system, and provided a simple and efficient histochemistry method for the AChE⁺ structure research in different planarians.