The utility model provides a lithology density microballon logging instrument coupling probe installs on the arm rest is promoted mainly to lithology density, and the polar plate is unanimous with the probe width and can realize lithology density and the well logging of the same orbit of microballon well logging simultaneously. Technical scheme: including coupling probe casing, microballon polar plate and coupling probe assembly, the coupling probe assembly includes electronic circuit, crystal, photomultiplier, wherein: be equipped with the axial cavity in the coupling probe casing, the coupling probe assembly is settled in the axial cavity, set up the elongated slot mouth with the coupling probe casing outside that the coupling probe assembly corresponds, the elongated slot mouth is sealed closing to connect by the microballon polar plate, the axial cavity open end of coupling probe casing is connected sealedly by sealed base, the tip outside is equipped with source room and source window under the coupling probe casing, the tip inboard is equipped with and prevents leaning out the protector under the coupling probe casing, it surveys window and short spacing detection window to be equipped with long spacing respectively at the last lower extreme that corresponds the face near microballon polar plate and axial cavity.