The Daerlong granitic complex in Linkou area is located at the convergence position of the Jiamusi and Songliao blocks. A systematic study of field geology, petrography, zircon U-Pb dating and wholerock major and trace elements has been conducted for the Daerlong granitic complex, aiming to determine its formation age, petrogenesis and tectonic setting, and further constrain the nature and evolution of the Mudanjiang Ocean. Field and petrographic observations show that the Daerlong granitic complex mainly consists of three rock types from old to young, i.e., biotite granodiorite, syenogranite and monzogranite. Geochemical data suggest that all the types of granitoids are high in silicon, rich in potassium, moderate in aluminum (A/CNK=0.94–1.10), poor in iron and magnesium, rich in LILEs and depleted in HFSEs, belonging to the weakly peraluminous high-K calc-alkaline series. Combined with mineral assemblages and geochemical discrimination diagrams, it can be determined that the studied granitoids are of igneous crustderived I-type origin, which underwent strong fractional crystallization and crystal accumulation during magmatic evolution. Zircon LA-ICP-MS U-Pb dating results show that the different types of granitoids were emplaced in a wide age range from 301 to 240 Ma, indicating a long-lived Late Carboniferous to Middle Triassic granitic magmatism occurred in the western Jiamusi Block. The Daerlong granitoids have similar geochemical characteristics of subduction-related igneous rocks. Considering the spatial and temporal distribution of Late Paleozoic to Early Mesozoic igneous rocks within eastern Heilongjiang Province, it is concluded that the Daerlong granitic complex was formed in an active continental margin setting rather than a continental rift environment. The results suggest that the Mudanjiang Ocean might not be a limited ocean evolved from the rifting of the uniffed Jiamusi-Songnen microcontinent.