A new calibration method of detectors by using correlated photons generated in spontaneous parametric down-conversion effect of nonlinear crystal is proposed. A CW ultraviolet (351 nm), diode-pumped, frequency-doubled, solid-state laser is used to pump BBO crystal. The degenerate parametric down-conversion (PDC) photons with wavelengths of 702 nm were produced and by tuning crystal angle, nondegenerate PDC photons with wavelengths of 633nm and 789nm were also produced. The quantum efficiencies of the photomultiplier at the above wavelengths were measured respectively. An absolute calibration system of detector quantum efficiency was performed. And its principle and experimental setup were introduced. The calibration uncertainties of PDC method were analyzed systematically. The results show the total calibration relative uncertainties are less than 5.5%. In the end, a comparison between PDC effect method and conventional method based on standard detectors was performed. The results show that the relative difference of the two methods is less than 10%.