The experimental results demonstrate that an amorphous colloidal crystal possesses a quasi-complete photonic band gap. The bandwidth and the wavelength of the forbidden gap in the amorphous crystal do not change along with the variation of the incident angle. The bandwidth of the stop band is much larger than that in the silica colloidal single crystal. The results also show that quasi-complete photonic band gap can be observed in an amorphous colloidal crystal with a low refractive index. The quasi-complete photonic band gap results from the fact that the symmetry of lattice is decreased in amorphous colloidal crystal.