Abstract: Calibration for the quantum efficiency of detectors is a new research subject. Spontaneous-parametric-down-conversion (SPDC) has the disadvantages of low conversion efficiency and signal noise ratio (SNR). In order to improve the power of correlation photon, a shortwave laser was used to pump the periodically poled lithium niobate (PPLN) crystal. The influence of incident angle on the conversion efficiency, spatial distribution, bandwidth and crystal poling period was analyzed based on numerical simulation. It is proved that the conversion efficiency is high, the bandwidth of correlation photon is narrow and the divergence angle is large for normal incident pumped beam. While the incident angle increases, the conversion efficiency becomes lower, the bandwidth and divergence angle are smaller and the position of central wavelength can shift. The result presented is a theoretical support for correlated photon detection and highly accurate calibration for quantum efficiency of detector.