Abstract: The two-dimensional(2D) metallic grating was introduced into the detector to improve the detection rate of Terahertz(THz) quantum well photodetector(QWP). The 2D metal grating simulation model of THz QWP was established by using the 3D finite-difference time-domain algorithm, the impact on the electric field strength of the 2D metal grating parameters of THz QWP was analyzed detailed. The results show that for the 6.27 THz (the corresponding wavelength is 47.847 m)incident light,the light electric field along the Z direction reaches its maximum and the grating coupling efficiency reached highest，when the grating parameters are taken as grating period P=10.5 m,dute cycle w= 5.755 m and grating layer thickness h=0.4 m