The diffraction properties of a volume grating for a pulsed laser beam with Gaussian-profile both in time and space domain are studied, using two-dimensional (2D) coupled-wave theory. Analytical expressions for the spatial and spectral profiles of the transmitted and diffracted beams are obtained. The influences of geometry parameter on the Bragg diffraction properties and the diffraction efficiency of the pulsed Gaussian beam are discussed. It is shown that the Bragg selectivity bandwidth and the diffraction bandwidth of volume gratings are broadened when geometry parameter g increases. The diffraction efficiency increases when pulse duration increases and trends to a saturated value, the smaller the geometry parameter g is, the slower the saturating velocity is, and the larger the saturation value is.