Abstract: In sedimentary basin, hydrothermal fluid flow can affect the redistribution of materials (e.g., minerals dissolve in fluid and hydrocarbon dissolved in a basin) and the localized thermal anomaly along the pathway systems (most often faults). Binhai fault is one of the main boundary faults that controls the source rock distribution in Qikou sag, Bohai Bay Basin, which provides a space for flow anomalies of hydrothermal fluid. The investigation of hydrothermal fluid flow in Binhai fault bases on geochemical characteristics of organic materials, fluid inclusions, natural gases, diagenetic minerals, and formation water. Evidences for hydrocarbon migration and accumulation along the fault were obtained, with which a favorable direction for hydrocarbon exploration was pointed out. Hydrothermal fluid flow along the fault has created the abnormal high temperature field near the fault. Changes in local temperature field related to hydrothermal fluid upwelling along the fault were illustrated by the following evidences: (1) Abnormal vitrinite reflectance indicates abnormal thermal evolution of local source rocks; (2) Fluid inclusions with higher homogenization temperature than that formed at the maximal burial depth of the basin; (3) Clay minerals experienced abnormal evolution, with multi-types in the same depth segment and the same type in multi-segments; (4) Thermal alterations occurred in clastic mineral particles of the reservoirs. Changes in the material field caused by hydrothermal fluid flow were illustrated by the following evidences: (1)Inorganic CO₂ originating from deep mantle and brought upward by hydrothermal fluid flow was enriched and accumulated in shallow; (2) Substantial high-salinity deep fluids penetrated and reacted with source rocks, leading to the accumulation of high-salinity formation water in reservoirs; (3) Multiple segments of secondary porosity zone were developed vertically, further demonstrating the occurrence of water-rock interactions. Secondary porosity zones were resulted from the dissolution and redistribution of carbonate minerals, which to some extent controlled the physical properties of reservoirs; (4) Water-rock interaction with substantial materials carried by thermal fluids led to abnormal enrichment of trace elements in rocks adjacent to the fault. Together the above evidences indicate that hydrothermal fluids migrated along the fault and permeable sandstone reservoirs in the study area, with great potential for oil-gas accumulation.