Abstract: In order to detect ［Ca2＋］i, a novel monochromatic source for the fluorescent microscope was designed. The system uses a short-arc Xenon lamp as light source. All the light is converged to a point source by the elliptical mirror. The point source is coupled into an optical fiber to form the monochromatic light output after collimating, light splitting and focusing by the blazed grating. In the illumination and excitation system of the fluorescence microscope, the light power and spectral purity of a monochromatic source are the two technical essentials，in which the aspherical reflector is the priority in design. The energy efficiency of the whole system was analyzed and calculated according to the optimization algorithm and the optical simulation. The elliptical reflector for the monochromatic source system was designed, and the complete equipment was developed. The experiment result shows that the elliptical mirror works in the whole system perfectly.