The invention provides a positioning device for implementing needle biopsy of breast tumor. The invention aims to solve the problems that an existing device cannot assist in fixing a soft breast during positioning, and tumor tissue is prone to displacement during puncture. The positioning device comprises a circular supporting disc, wherein the outer side of the supporting disc is rotationally connected with a plurality of double-layer extrusion devices, the upper end of the supporting disc is provided with a supporting rod, the supporting rod is slidably connected with a moving seat, a structural hole is formed in the axis of the bottom of the supporting disc, an avoiding groove is formed in the side wall of the supporting rod, and a suction cup device is arranged in the structural hole and the avoiding groove; a puncture needle guiding device is arranged on the side edge of the supporting disc, and a rotating sleeve is rotationally connected to the upper end of the supporting rod and fixedly connected to a main support body; and a double-layer extrusion device comprises an outer-layer plate rotationally connected to the side edge of the supporting disc, the outer-layer plate is in an arc shape, an inner-layer plate is hinged to the lower end of the outer-layer plate, a tension spring is arranged between the outer-layer plate and the inner-layer plate, a sliding rail is arranged at the upper end of the inner-layer plate, clamping teeth are arranged in the sliding rail, an extrusion rod is rotationally connected to the outer-layer plate, and the lower end of the extrusion rod can be clamped with the clamping teeth.