To enlarge the steering range of optical phased array, volume holographic grating is employed to act as amplifier stage. The influence of structure parameters and fabrication errors on the performance of grating is studied, and tolerance optimization is proposed to reduce the influence. The results show that grating thickness and refractive index modulation are main parameters that affect diffraction efficiency; grating period and thickness are main parameters that affect angular selectivity. Bragg angle and diffraction angle are determined by grating period and grating vector slant angle, which can be adjusted by rotating medium in the incident and diffraction plane if the angular magnification keeps unchanged. In fabrication process, grating period error and grating vector slant angle error will make diffraction angle diverging design value. The longer readout beam wavelength is, the less impact grating period error has; the higher medium refractive index behind grating is, the less impact grating vector slant angle error has. Increasing grating thickness design value can reduce the impact of grating thickness error on diffraction efficiency, while reducing grating thickness design value can reduce the impact of refractive index modulation error on diffraction efficiency, so it′s necessary to combine with the optical phased array system′s requirements to make integrated design.