The utility model relates to a multi-head mirror milling device for a cylindrical thin-walled workpiece. In order to overcome the deficiencies that the existing mirror milling device usually has a single-cutter head which difficultly meets the high-precision requirement of a large cylindrical thin-walled workpiece and is low in working efficiency, a central stand column is fixedly arranged at the circle center of a base, a top positioning tool is arranged on the upper end of the central stand column, and a top adjustable workpiece clamping mechanism is arranged below the top positioning tool; a bottom positioning tool is fixedly arranged on the base, a bottom adjustable workpiece clamping mechanism is arranged above the bottom positioning tool, an internal stand column is arranged on a circular track of the base, and a milling electric main shaft assembly is arranged on the outer side of the internal stand column; an external stand column is arranged on the excircle track of the base, and a follow-up ejecting assembly is arranged on the inner side of the external stand column. The multi-head mirror milling device has the beneficial effects that the design is reasonable, low-rigidity cylindrical thin-walled workpieces are conveniently installed, positioned and adjusted; the shape precision, position precision and size precision of the processed workpieces can be guaranteed, and the processing efficiency can be greatly increased.