The artificial opals are three-dimensional photonic crystals (PCs) whose microspheres are arranged periodically in a face-centered-cubic (FCC) lattice. In this work, we investigated the reflective properties of artificial opals composed of submicron silica spheres. The finite-difference time-domain (FDTD) method for electromagnetics was used to calculate the directional–hemispherical reflectance spectra of artificial opals. Factors including structural parameters, filling dielectrics, and incident light were considered to study their effect on the reflectance. It is found that the shape, value, and position of peak of the reflectance spectra can be affected by these factors. Furthermore, by analyzing the distribution and propagation of the Poynting vectors at normal incidence of P-polarization, the high reflectance of artificial opals can be attributed to the fact that reflected light from parallel crystal face generates constructive interference to strengthen the total reflected beam. As to the engineering applications, we performed a detailed analysis of the detection sensitivity of artificial opals acting as a chemical sensor. It is found that the diameter of the spheres of artificial opals has a prominent influence on the detection sensitivity which is improved with the increase in the diameter of the spheres. This work will facilitate the design, manufacture, and application of artificial opals.