A 16-element focal plane linear array (FPLA) operating at 84～94GHz for passive millimeter-wave imaging was designed. The parabolic reflector with 500mm diameter was used to obtain an angular resolution of 0.47?. The 16 feed-horns are arranged as 4×4 array and the adjacent feed-horns are stagger at vertical direction, which doubles the scene sampling density in vertical direction and satisfies Nyquist theorem. The radiation field of the antenna was calculated in MATLAB by using current distribution method, and the location of the feed horns was optimized based on the results. Imaging results indicate that the full sampling imaging data of scene can be obtained when the FPLA scanning is done in horizontal direction for only one time and imaging time is reduced to half that of the traditional scanning way.