The utility model relates to an oil mass sensor, which belongs to oil mass sensor technology field. the object of the utility model is principally to resolve defects of circuit board corrosion and guide rod fracture due to water and oil entering the inner of the existing straight-tube type oil mass sensor. The oil mass sensor is characterized in that it includes an end button assembly, a flange disk, a seal washer, a guide rod, a float assembly, and a reed switch circuit board assembly; the flange disk and the bottom board are made of metal material identical to that for preparing the guide rod, and are welded on two ends of the guide rod; locating grooves and locating small bosses for installation are arranged between the end button assembly and the flange disk; the connection portion of the flange disk and the end button assembly is provided with large bosses, and the end button assembly is provided with grooves matching with the large bosses. the utility model has characteristics of real-time detection and monitoring oil mass of an oil tank, high precision, reliable quality and long durability, and is principally used for straight-tube type oil mass sensor to automatically detect remnant oil mass of an automobile oil tank.