Abstract: The present disclosure provides a precision calibrating device and a precision calibrating method for a magnetorheological polishing device, which realize an automatic and quick calibration process. It is ensured that a polishing gap is kept within an allowable error range when the magnetorheological polishing device processes surfaces of different optical elements, thereby effectively controlling a removal function, reducing or eliminating surface residual errors after processing and low frequency errors and medium frequency errors introduced by insufficient trajectory precision of a mechanical arm, and improving a processing precision of the magnetorheological polishing device based on the mechanical arm.