Abstract: As an important part of the western Pacific convergent marginal basin system, the origin and movement history of the East China Sea Basin is still controversial, especially the paleopositional relationship between the East China Sea and the South China Block, which remains unclear. To clarify the paleolocation changes of the East China Sea Basin since the Early Cretaceous, we conducted a systematic paleomagnetic study using Cretaceous-Eocene samples from nine boreholes in the East China Sea Basin. Results show that the East China Sea Basin was located at a low latitude between 15°N and 30°N during the Early Cretaceous to Middle Eocene epoches, and its paleo-orientation was largely the same to the modern one, showing a close paleogeographical relationship and tectonic affinity with the South China Block. The comparative analysis of the paleoposition of the East China Sea and South China Block showed that the East China Sea had always been located in the southeast of the South China Block from the Early Cretaceous (~134 Ma) to the Middle Eocene (~40 Ma). During this period, the latitudinal difference between the two had continued to narrow down, and their positions became closer after experiencing three stages of change: (1) From the Early Cretaceous to the Early Paleocene (~134 - ~65 Ma), the latitudinal difference between the East China Sea and South China Block decreased slowly from 9.0° to 6.2°; (2) from the Early Paleocene to the end of the Middle Paleocene (~65 - ~60 Ma), the latitudinal difference between the two decreased rapidly from 6.2° to 1.2°; (3) from the end of the Middle Paleocene to the Middle Eocene (~60 - ~40 Ma), the latitudinal difference ranged from 1.2° to 2.0°, and a spatial pattern similar to the modern one was formed between the East China Sea and South China Block, with synchronous movement. This study confirmed the tectonic affinity between the East China Sea and the South China Block since the Early Cretaceous, holding significant implications for research on the tectonic evolution of the East China Sea Basin and the evaluation of its hydrocarbon resource potential.