Currently, optical sensors usually need to build high-accuracy primary standard, and then transfer to user sensor based on a series of comparison chain, the precision of primary standard and standard transfer chain are the major sources of uncertainty. Combined with parametric downconversion method, theory and experiment results in recent years at home and abroad, the advantages of absolute sources and detectors of parametric downconversion are referred. Considering the need of practical application of calibration technique of parametric downconversion, the necessity, technique difficulty and solution of calibration technique of parametric downconversion are introduced when calibration technique of parametric downconversion transfers to broad band and analog detectors.