The utility model discloses a wellhead expansion device for mining exploration. Including a dilator body, the dilator body is composed of two clamping mechanisms. The upper edge of the clamping mechanism extends outwards, conical protrusions with the tops facing downwards are evenly distributed on the lower portion of the upper edge of the clamping mechanism, the lower portion of the clamping mechanism extends downwards, a semi-arc-shaped limiting base extending outwards is arranged on the outer wall of the lower edge of the clamping mechanism, and a groove is formed in the upper surface of the upper edge of the clamping mechanism. A grating plate is arranged above the groove, the grating plate is of a semi-arc-shaped structure, through holes are formed in the surface of the grating plate,and the upper surface of the grating plate is flush with the upper surface of the upper edge of the clamping mechanism where the groove is located. The device is firmly clamped to the ground around the wellhead through the clamping mechanism, the placement stability of the clamping mechanism is improved, dust pollution is reduced through the arrangement of the grooves, and constructors can directly observe or construct detection instruments in an exploratory well from the device conveniently.