A wide-field imaging spectrometer based on a grating prism is proposed. The grating and prism parameters are discussed to balance spectral distortion over the entire band. The design method of the grating-prism (GP) dispersive module and the catadioptric optics of the spectrometer are discussed in detail. A high optical speed (F/2.4) and long slit (29.4 mm) visible and near-infrared design with high image quality and small distortion is presented. The results show that the optical performance of the GP imaging spectrometer is excellent. The tolerance analysis indicates that the GP spectrometer can be easily manufactured and implemented. The prototype has been tested in the laboratory and outdoors, and the results confirmed that the design will be useful in the fields of aeronautics and astronautics.