The dependence of the resolution of a fluorescent confocal microscopy on fluorescent spectrum is studied, and the power transfer function and three-dimensional pulse spread function are derived. Assuming well-distributed fluorescent spectrum, calculated results show that the lateral resolution and the Axial resolution are worse while fluorescent spectrum widen and dispersion coefficient increased, compared with that by only using the central fluorescent wavelength. The detector responding to narrower fluorescent spectrum is good for the resolution.