Convex blazed grating is one of the most important devices in hyperspectral imaging spectrometers. The major application obstacle is the huge gap between the diffraction efficiency which is obtained from the experiment and that in theory. The bottleneck lies in the small blazing angles required in the manufactory. To solve this problem, a convex blazed grating is made by adopting an argon ionbeam to directly etch the substrate through a photoresist mask. Considering the potential inconsistent blazing angles across the whole convex grating area with big glancing angle, the blazed grating etching of spherical surface is realized by using a circular scanning etching. A grating of a small blazing angle of 4.3° is fabricated. The average efficiency of the first order diffracted beams is more than 40% in the visible wavelength range.