The Tongjiang- Yuejinshan accretionary complex, located on the western margin of the Jiamusi massif in NE China, has great significance for reconstructing the subduction- accretion process of the Paleo- Pacific oceanic plate. However, the formation time of the ancient ocean and its tectonic affinity, as recorded in this complex, remain poorly constrained. Based on our geological survey, we present new geochronological and geochemical data from mafic igneous blocks in the complex. In the Yuejinshan Complex, in- situ zircon U- Pb dating of basalt yields a mean age of 314±2 Ma with ocean island basalt (OIB)- like geochemical signatures. Within the Tongjiang complex, a plagioclase amphibolite yields a zircon U- Pb age of 272±2 Ma and shows mid- ocean ridge basalt (MORB)- like major and rare earth element patterns, while another basalt sample exhibits fore- arc basalt (FAB)- like geochemical features. Combined with previous research, these results indicate that the Tongjiang- Yuejinshan accretionary complex formed during the Permian to Late Triassic, recording the subduction- accretion of the Paleo- Pacific ocean plate.