A reproducible color gamut in CIE L*a*b* 3D color space is proposed as a performance index for evaluating the reproducibility of dichroic filters used in color separation/recombination system. Using this method, the effect of broad conic angle incidence on the color reproducibility from the special angle characteristic of dichroic filters is analyzed. And from the viewpoint of optimizing the volume of the color gamut, a precompensation method is presented to optimize the filters′ design parameter so that the color reproducibility of the films will be promoted remarkably when the incident beam is broad conic angle beam.