A visible near infrared imaging spectrometer, which is mounted on the unmanned aerial vehicle, was designed for ground objects spectral analysis. The prism-grating-prism structure used in the spectrometer has the advantages of coaxial installation, small size and light weight. Objective lens with large field of view was designed through angular magnification selection, optical focal length distribution and relative aperture calculation. Initial spectral system structure was designed based on grating equation solution, volume phase holographic grating Bragg condition constraint and prism refraction law. The focal length of the objective lens was determined by the relationship between the emission angle and the detector width. The nonlinearity of the emission spectrum was shown by the exit light angle. The designed unmanned airborne imaging spectrometer has the spectral range of 400~1 000 nm and the filed angle of 40°. The transfer function value is greater than 0.67 in the whole spectral range at the cut-off frequency of 20.8lp/mm, and the spectral resolution is less than 3nm. An unmanned airborne imaging spectrometer was assembled for spectral push broom imaging experiments on trees outdoors，and the multi-spectral image of leaves was obtained. The imaging spectrometer can effectively realize spectral imaging, and has good performances.