Aiming at the performance requirements of a DMD-based Offner spectral imager encoding in spectral dimension for a convex blazed grating, a macro-micro integrated optimization design method for convex blazed gratings was proposed. The three-dimensional polarization ray tracing algorithm was used to organically integrate the optical design of the Offner system in macro-level and the groove design of the convex blazed grating in micro-level. The composition and working principle of the coded aperture Offner spectral imaging system were introduced, and a MWIR convex blazed grating with an average diffraction efficiency of 85.47% was designed according to the requirements of the system. On this basis, a convex blazed grating with curvature radius of 120 mm, grating period of 99.945 μm, blazed angle of 1.1783°, groove depth of 1.834 μm was successfully fabricated by using an ultra-precision single-point diamond lathe. The test results show that in the spectral range of 3-5 μm, the maximum diffraction efficiency is 93.46% and the average diffraction efficiency is 84.29%, which is in good agreement with the theoretical design value. Thus, the proposed design method of the convex blazed grating is verified to be effective and valuable.