Abstract: Based on the 2D seismic, magnetic and well data, we studied in this paper the characteristics of the igneous rock in the Jiulongjiang Sag of the Taiwan Strait Basin, the relationships of the magmatic activity with the regional tectonics and the sag evolution, and their petroleum significance. The JiuLongJiang Sag has suffered from two times of volcanic activities. Three types of seismic facies of igneous rocks, the tabular, conical and massive igneous rocks, are recognized in seismic profiles. The well data reveals that there are three types of igneous rocks i.e. extrusive rock, intrusive rock and volcanoclastic rock. The development and the distribution of the igneous rocks are related to the regional tectonics and basin evolution. The magmatic activity in Late Eocene is supposed favorable for a large quantity of hydrocarbon to generate from source rocks, as the high thermal fluid brought by magmatism could increase ancient geothermal gradient and accelerate the evolution of source rocks towards maturity. The igneous rock walls could result in the formation of more conduits for oil and gas migration and accumulation. The porosity and permeability of reservoir could be improved and the metamorphism of the reservoirs maybe helpful to the improvement of reservoir properties. It is a matter of concern in the future oil exploration and development.