The Lengshui volcano-intrusive complex occurs in the Mesozoic volcanic depression of the northeastern Jiangxi province. Its country rocks are mainly metamorphic rocks of Banxi Group. This complex consists of extrusive rocks which are mainly rhyolite-pyroclastic rocks, different kind of subvolcanic rocks and shallow-plutonic rocks from the basic basalt-porphyrite to the acidic granite-porphry. It belongs to a calcalkalie rock series, but it exhibits some features of the potash-rich subalkalic rocks formed at the late stage of the magmatic differentiation. The regularity in the development of the zoned magma chamber can be seen in the perfect fractional crystallization, gravitational differentiation and intrusive sequence. The Rb/Sr and Li/Mg ratios of the rocks increase, while the Ba/Rb ratio decrease with the evolution of the petrochemical composition from basic to acidic. The content of siderophile elements is quite low and that of chalcophile elements is high in the complex in comparison with the same kind of rocks in South China. The REE distribution patterns of the rocks show similarity with the syntectic granitoid in South China. The initial ratio of (87)Sr/(86)Sr is 0.7139. The rock-forming materials originated mainly from partical melting of lower crust of the earth. The authors have concluded that the volcano-intrusive complex is comagmatic rock and it is resulted from the different evolvementary stage of the s yntectic magma.