Offner imaging spectrometer consists of a convex grating and two concave mirrors. The concentric characteristics of the optical structure make it have the advantages of large relative aperture, small distortion and compact structure. In order to reduce the alignment difficulty of the Offner imaging spectrometer and improve the efficiency, a fast alignment method of Offner imaging spectrometer is presented in this paper based on the concentric characteristic and spherical autostigmatic method. Firstly, the spherical autostigmatic device is built, which can generate point source, and when the point source is located at the spherical mirror’s center of curvature (CoC), its reflection image point and the point source coincide. By measuring the distance between the reflection image point and the point source, the position deviation of the spherical mirror’s CoC can be determined. The Offner imaging spectrometer is completed with this device by locating the CoC of its primary mirror, convex grating and tertiary mirrors. The results show that location error of the two off-axis concave mirrors’s CoC can be controlled within 10μm, and the imaging performance of the imaging spectral system is satisfied. Compared with the existing method, this method has the advantages such as easy to operate, low cost and fast alignment.