Fluorescence power transfer function, three dimensional point spread function (3D PSF) and three dimensional optical transfer function (3D OTF) for the various fluorescent wavelength are calculated. The results show that the fluorescent wavelength has influence on imaging property of confocal microscopy such as spatial cut off frequency, resolution and 3D OTF. There is a missing cone in the 3 D space of OTF when the ratio of excitation wavelength to fluorescent wavelength decreases.