The present disclosure discloses a calibrating method, apparatus, and corresponding measurement system for a composite waveplate. The calibrating method comprises: A. determining a first matrix characterizing the composite waveplate, the first matrix including at least one unknown number; B. determining a theoretical relationship between a light intensity and an alignment angle offset value of the composite waveplate based on the first matrix; and C. calibrating based on the theoretical relationship between a light intensity and an alignment angle offset value of the composite waveplate determined in step (B) and actually measured light intensity data to obtain a second matrix that may characterize the composite waveplate and does not contain the unknown number. The technical solution of the present disclosure may greatly reduce the amount of unknown numbers when calibrating a composite waveplate or a measuring system, thereby lowering the difficulty of calibration and improving the precision of calibration.