Utilizing the image of spatial filter’s pinhole of high power laser systems and diffraction of sample grating, with an insertable negative lens for the pinhole’s on-axial illumination, a new system for far-field detection of laser beam is presented. This far-field detection system, which is fully demonstrated on the experimental system, can fully use space through off-axial grating sampling. The experimental results indicate, that the average far-field alignment error is less than 1.42% of spatial filter pinhole diameter, which meets the alignment system requirements (5% of spatial filter pinhole diameter).