A depolarizing dichroic beam splitter, which works in the waveband from 350 nm to 1700 nm is designed and fabricated for broadband imaging spectrometers. Based on the working characteristics of the imaging spectrometer, the spectra in near-UV, visible and near-infrared bands are effectively separated, and the signals spread to their respective focal planes and are received by different detectors, respectively. In order to achieve high reflectance from near-UV to visible, two thin film materials are selected to structure four reflectance stacks. The linear polarization sensitivity is hard to control because of absorption of the thin film materials, and the problem is solved by adjusting the order of stacks. The spectra in the transmission band are smoothed by the non-regular film matching. The optical efficiencies in the reflection and transmission bands are as high as 97% and 91%, respectively, and the linear polarization sensitivity is lower than 1.5%.