Structure characters of a dualchannel helmet mounted display （DCHMD） optical system was analyzed. Based on the discussion of the requirements of DCHMD in application, the system′s technical specifications were presented. The offaxis aberration was analyzed and corrected by proper freeform surface at the right place of the optical system. A DCHMD optical system was developed with technical specifications: 40\O×30\O field of view, 15mm exit pupil diameter, 26.4 mm effective focal length, 25 mm eye relief distance, wavelength range 540~560nm, back focal length more than 3 mm and modulation transfer function (MTF) higher than 0.1 at the frequency of 0.88 lp/mrad. This system has a compact size (70 mm×122 mm) and a decent center of gravity, and could be embedded in the helmets.