A new photoelectric model of silicon based position sensitive detector(PSD) is built and the formulas of the photocurrent and spectral response are gotten with it.The effect of every layer thickness and SiO_2 thickness on the spectral response is analysed and calculated.The spectral response of PSD is affected by the thickness of p layer mainly at short wavelength and by the thickness of the depletion layer mainly at long wavelength.With the results,a new silicon based near infrared 2-D pincushion PSD is designed and fabricated.The experimental results show that the peak spectral sensitivity of our device is 0.626 A/W at 920 nm wavelength.