Based on Kogelnik’s one-dimensional coupled-wave theory and dispersed Fourier transform, the diffractive characteristic of two pieces of volume phase gratings, which are cascaded and having orthogonal grating vectors for the continuous-wave (CW) laser beam, is analyzed. The cascaded gratings’ low-pass spatial filtering for CW laser beam is performed. And the performance of its filtering for deformed Gaussian laser beam is simulated. The results show that with the fine angular selectivity of volume grating, the component of the larger quantity in angular spectrum domain can be deleted directly without focusing the laser beam. The distribution of intensity of diffractive laser beam is similar to that of the undeformed one in spatial domain. So the low-pass spatial filtering for CW laser beam is realized. This novel method can eliminate the drawbacks of pin-hole filter, which focuses the laser beam, enhances its intensity in the focal plane, and probably damages the stuff vicinal to the pin hole. So it may take the role of the pin-hole filter, especially in the high-power laser field.