Abstract: Image basins and hydrocarbon fluids are developed during the evolution of the earth under sphere movement and gravitational differentiation. Hydrocarbon fluid exists in the mantle fluid in the spheres of the earth and it is a kind of supercritical heat generating and transporting fluid with high compression, high density and high energy. It is composed of organic compounds with extremely strong reducing property, and the components are H, H2, CH4, and CO. The earth has four high pressure gas-spheres al least, such as the gas-sphere in the outer core, the gas-sphere in the upper mantle, the gas-sphere in the middle crust, and the gas-sphere in the upper crust, The hydrocarbon fluid in the gas-sphere features in high energy, high pressure, high temperature, strong chemical activity, and high penetrating capacity. Lower image basins are the best choice for storing hydrocarbon sources. To find low-velocity bodies in upper image basins where deep large faults developed and correspond with each other is the basis for discovering large oil and gas fields

Key words: image basin, asthenosphere, hydrocarbon fluid