Based on Fourier transform, the ultra-short pulsed Gaussian laser beam is transformed into linear combinations of monochromatic plane waves. Depending on Kogelnik′s one-dimensional coupled-wave theory, the diffraction characteristics of monochromatic plane waves by transmitting volume grating are put forward, when the central wave vector satisfies the Bragg condition of the volume grating. With the inverse Fourier transform of diffraction of monochromatic plane waves, the law of spatial and temporal intensing distribution of diffractive beam with different parameters of volume grating is given. The results show that diffractive laser beam is broadened in the temporal and spatial domains, in the plane comprising of the grating vector and the normal vector of the grating front surface, with the decreasing period of the transmitting volume grating. Its broadening trend in the spatial domain is faster than that in the temporal domain. Compared with input ultra-short pulsed Gaussian laser beam, the diffractive laser beam is deteriorated obviously in the spatial domain. Diffractive laser beam is broadened in the temporal and spatial domains in the plane comprising of the grating vector and the normal vector of the grating front surface, with the increasing thickness of the grating. And its broadening trend is equal to each other in the spatial and in temporal domains. Compared with the input ultra-short pulsed Gaussian laser beam, the diffractive laser beam is deteriorated both in the temporal and spatial domains.