A dual concave gratings imaging spectrometer with excellent imaging ability in near infrared waveband has been presented. The main aberrations as astigmatism and coma have been analyzed existing in this tandem gratings system. By calculating, the best imaging conditions, the optimal arrangements of gratings and adding cylindrical lens, were obtained. The advanced Wadsworth mounting could eliminate coma and astigmatism in the wide waveband and realize the high imaging quality. It could also realize the high spectral resolution with low ruling density gratings. A designed example presented excellent optical performances, the spectral sampling was 0.92 nm per pixel and modulation transfer function in all fields of views were higher than 0.45 in the Nyquist frequency at 17 lp/mm over the waveband from 780 nm to 1 100 nm. The aberrations of the system were corrected and the tolerances were loose. The results analysis proves the principle of design.