The invention discloses a concave volume holographic grating which comprises a volume holographic grating body. The front surface of the volume holographic grating body is provided with an arc groove; and a curve obtained through rip cutting of the arc groove meets the following condition: (n-1)arctan f'(x)-arctan((x-a)/(f(x)-b))+arctan(a/b)=0, wherein the x axis is a coordinate axis tangent with the lowest point of the curve, the y axis is a coordinate axis perpendicular to the bottom surface of the grating, the f(x) represents a curve equation, the f'(x) is a first-order derivative of the f(x), the n is grating medium refractive index, and the a and b are the horizontal coordinate and vertical coordinate of a light source respectively. Through the structure above, angle requirement for incident rays can be reduced, the step of parallel light processing is saved, and complexity degree of the device is reduced.