We present the optical characterization of quantum dot cascade laser (QDCL) structures using photoluminescence. In this work, two InAs/AlAs quantum dot structures are investigated with different GaAs QW thicknesses. Low temperature photoluminescence measurements show peaks at 1.03 eV, 1.28 eV, and 1.51 eV for QDCL1, and 1.07 eV, 1.27 eV, and 1.47 eV for sample QDCL2, corresponding to ee-hh transition in both QD and QW. A three dimensional QD-QW model in Nextnano is developed to simulate the energy states, wave functions, and transition rates between conduction and valence bands using a typical QD size obtained from atomic force microscope measurements. The simulation results agree well with the experimental data. This allows us not only to understand the optical characteristics of the QD-QW structure, but also to optimize the QDCL structure design.