The invention provides a natural electric current logging instrument which comprises a logging ground system, a signal processing short joint, a pushing backup device, a control circuit short joint and a measuring polar plate, wherein the signal processing short joint, the control circuit short joint and the pushing backup device are serially connected through threads, and the measuring polar plate is connected with a pushing backup arm of the pushing backup device. According to the invention, the measuring polar plate made of an insulating rubber material is adopted, a measuring electrode is embedded in a groove of the measuring polar plate, the measuring polar plate is clung to a well wall at a logging moment, the flow of natural electric current between slurry and ground layers and between the upper and lower ground layers is isolated, a natural electric current measuring circuit is serially connected between the two electrodes of the measuring polar plate, and a higher logging curve resolution ratio is acquired, so that the film layer dividing, thin interlayers and interlayer subdivision are realized; the permeability of rock stratum is analyzed and calculated; matched with other logging methods, the instrument can be used for accurately dividing water flooded levels of a water flooded layer and calculating oil saturation and other oil-layer parameters are.