Aiming at the wide-spectrum high-resolution echelle spectrometer, the dispersion characteristic of the echelle grating and the cross-dispersion principle is discussed. And an optical design method of resolution preferential echelle-prism cross-dispersion is described, including the design of high-resolution main dispersion, the auxiliary dispersion for the separation on the overlapped orders, and the main-auxiliary dispersion calibration and revision. According to the requirements of commercial spectrometer, a design example is reported. The simulation and the experiment results show that when the spectral span is 400～900 nm, the resolution for Hg 546 nm is 51 000, and that for Na 589 nm is 44 000.