Abstract: Conventional see-through head-mounted displays can display virtual image; however, virtual image can not keep clear on the retina from beginning to end when the eyes adjusts the focus length.So a new technology of see-through head-mounted displays which can catch sight of external features and see the virtual image on the micro-display chip has been introduced. It is an advantage of virtual image, which can always keep clear, no matter how to adiust the focus of eyes. The principle of display technology was discussed.The overall optical system was designed by using Zemax and reached the diffraction limit after optimization.The MTF of filtering projection system was 0.7 at 60 lp/mm. The structure of head-mounted displays was designed by Autocad. The imaging experiment result shows that both the external features and the virtual image could be seen clearly in the presence of eyes focusing on external features. Though the external features would be fuzzy when eyes defocus on external features, the virtual image could still be seen as clearly as before.