Research on spectrum distribution of correlated photon optics-field has great significance in terms of the calibration for photoelectric detector in broadband spectrum based on spontaneous parametric down-conversion. An experiment is set up to measure the distribution of correlated photon broadband spectrum. A continuous wave 355 nm laser and a photon counting system are used to pump the β -barium borate (BBO) crystal to product type I spontaneous parametric down-conversion in the regime of nonlinear and the spectrum distribution of correlated photon outside the BBO crystal is measured, respectively. The bandwidth of correlated photon spectrum in experiment is 259 nm (550~808 nm). The angle distribution result in experiment is in accordance with the theory prediction, with the angle distribution difference less than 2%. It is turned out that a broad band spectrum distribution from visible to near infrared exists with respect to correlated photon. It is promising to be applied to calibration for photoelectric detector in broadband spectrum.