The sub-structure in absorption spectrum was analyzed by means of photoluminescence excitation (PLE) spectra. The glass samples of CdSeS quantum dots were prepared by co-melting and analyzed by means of high resolution transmission electron microscopy (HRTEM), the annealing time was 2 h and 4 h respectively, the quantum dots' diameter was 3.6 and 3.8 nm respectively. Absorption spectra and photoluminescence excitation spectra were measured at room temperature. The absorption spectra showed quantum size-dependent effects. Two peaks were observed in photoluminescence excitation spectra. The valence band degeneracy and the interaction between electrons and holes were taken into account, the energies of 1S3/2-1Se and 2S3/2-1Se transitions versus quantum dots' radii were obtained by theoretical analysis and numerical calculation. The two peaks in photoluminescence excitation spectra are assigned to 1S3/2-1Se and 2S3/2-1Se transitions, respectively.