In the process of preparing entangled photon pairs by spontaneous parametric conversion technology based on second-order nonlinear effects, the periodically polarized crystals doped with 5 mol%MgO:PPLN were studied. By linking the momentum conservation and energy conservation conditions in the process of optical parametric transformation with the dispersion equation of the crystal and the thermal expansion equation of the crystal polarization period with temperature, the period-tuning and temperature-tuning properties of entangled photon pairs were obtained at the five commonly used wavelength points of 355 nm, 405 nm, 532 nm, 780 nm and 1 064 nm. It was found that the crystal polarization period was too small and two pairs of entangled photon pairs were generated during the research process, and the entangled light band range generated by the interaction of each wavelength point with nonlinear crystals under a certain polarization period and temperature was summarized. When other nonlinear periodical polarized crystals were selected for experiments, the polarized periodic term in the QPM momentum conservation condition was changed, and the dispersion equation was changed according to the specific crystal used. This research scheme can be directly extended to the research of using different nonlinear crystals to generate entangled photon pairs in the communication optical band or infrared optical band, and has important research value in the field of preparing quantum light sources.