Ion beam etching technology was researched for fabricating blaze concave gratings, and a partitioned space calculated method was proposed to calculate the diffraction efficiency of a blaze concave grating. The method can calculate the diffraction efficiency quantitatively without experimentation by confirming an incidence angle. The blazed angle of the blaze concave grating with a given wavelength was calculated based on the partitioned space calculated method, and ion beam etching parameters and a mask parameter were calculated by etching software BLAZING. On the basis of these parameters, a concave grating with a size of 45mm×40mm was fabricated by holographic ion beam etching. The focus blazed angles measured by an Atomic Force Microscope(AFM) are 9.21°,the efficiencies of the gratings measured by a concave grating diffraction efficiency instrument are about 54.8% at 300 nm and 50% at 250 nm. The grating substrate has a smooth blazed groove profile with 1 200 groove/mm. The results are in agreement with that partitioned space calculated well. It means that partitioned space calculated method is suitable for designing and calculating the efficiency of blaze concave gratings and it can direct the fabrication of the blaze concave gratings by the ion beam etching technology.