A fast assembly method of an Offner spectral imaging optical system. The Offner spectral imaging optical system is a concentric or nearly concentric optical system, that is, its primary mirror (7), convex grating (5) and three-mirror (8) are all spherical, and respective centers of curvature coincide or basically coincide. Based on the self-collimation principle, the invention quickly determines the position of the center of curvature of the spherical mirror by observing the self-collimation image after the point light source is reflected by the spherical mirror. The assembly and adjustment method provided by the invention has the characteristics of fast assembly and adjustment speed, high precision, low requirements for assembly and adjustment environment and low required equipment cost, and can quickly and effectively complete the assembly and adjustment of the Offner spectral imaging optical system.