Characterization of colloidal crystals composed of two types of polystyrene particles of different sizes (94 nm and 141 nm respectively) at different number ratios is studied by means of Kossel diffraction and reflection spectra technique. The results showed the dependence of the mean interparticle distance (D0) and crystal structure on the number ratio of the two types of particles. The formation time of crystals lengthens as the number ratio of the two components approaches 1∶1. When the number ratio (9 4nm∶141 nm) decreases, the mean interparticle distance (D0) becomes larger. This study also shows that when the above number ratio equals 5:1, superlattice structure appears in the binary colloidal system.