Pulse compression gratings based on multilayer dielectric film or metal multilayer dielectric film usually work around the Littrow angle with high diffraction efficiency and broad diffraction band. There is a large requirement to have high resolution and accurate measurement on the grating diffraction spectrum in the purpose of optimizing the fabrication process. Based on the double light paths system, an optical characterization method and the corresponding setup with high spectral resolution for broadband high diffraction efficiency pulse compression gratings are demonstrated. The method to eliminate the influence of the background and the light source fluctuation is discussed in detail. Two practical problems are perfectly settled, including the large spot size of diffracted light which is not completely collected by optical detector and the detector blocking of the incident light near the Littrow angle. The setup can measure the reflection and transmission diffractive spectra for each diffractive order of broadband pulse compression gratings, as well as the angular spectrum with fixed wavelength. The setup can measure the grating diffractive spectrum with resolution of 1 nm and the grating angular spectrum with resolution of 0.2° at present. The optical spectrum and angular spectrum of pulse compression grating samples are measured on the established measurement setup. Diffraction efficiencies greater than 90% in the wavelength range of 770~870 nm are obtained with measurement error no more than 2.2% and average relative deviation no more than 1.0%.