Dual-DMD based MWIR spectral imaging system encoding in spectral dimension was proposed, the tilt of image plane offset caused by the spectral encoding DMD was compansated by a DMD which in the spatial dimension. The composition and working principle of the system were introduced. As a front imaging unit, the telescopic system with a focal length of 240 mm and a F number of 3 was designed. The dual-pass Offner spectroscopic system and the spectral encoding DMD were used to realize multiple functions such as dispersion, encoding, and recombination. A relay imaging system with a magnification of 1 was designed to achieve strict matching of the cold stop. Through the integrated optimization design, the remaining aberrations of the dual-pass Offner spectroscopic system was compensated. The result of designing shows that the system has good spatial imaging and spectral performance, and the operating distance meets the design requirement.