A calibration method for a coordinate system of a workpiece held by a robot manipulator, which includes the following steps: setting a predicted coordinate system on the workpiece; controlling the drive mechanism to drive the workpiece to move a specific distance along a coordinate axis in the predicted coordinate system and measuring the distance change of the workpiece in a direction perpendicular to the move; using the measured distance change to determine an orientation error between the predicted coordinate system and the actual coordinate system; correcting the orientation parameters of the predicted coordinate system; controlling the drive mechanism to drive the workpiece to rotate by a specific angle around a coordinate axis of the predicted coordinate system and measuring the distance change after being rotated; using the measured distance change to determine a position error; correcting the position parameters of the predicted coordinate system.