Send gamma rays to the formation via the 137Cs gamma ray source mounted on the instrument, the instrument detector measures the amount of the gamma-ray photon reaching the instrument after formation attenuation, and calculates to obtain the formation density and photoelectric absorption index. The instrument adopts Cs-137 gamma ray source and NaI crystal counter, and is equipped with 16-sector azimuthal measurement imaging technology, and is installed with ultrasonic transducer for clearance detection and compensation calculation.