500nm AlGaN thick layer with AlGaN/GaN MQW interlayer was grown on sapphire substrate for UV detector and resonant tunneling diodes by MOCVD equipment. We were strongly interesting in the stress information of QW. There are a big mismatch of lattice between AlN and GaN.The growth of thick and high quality AlGaN is difficult task. AlGaN/GaN MQW layers were designed to relax the big mismatch stress. Many researcher focused on the stress relax mechanism for the growth of AlGaN alloy. The stress in QW can change the band gap structure and carrier contents of polarize induced charge. Raman spectra were a useful tool to observe the stress of semiconductor materials without damaging the sample. Using 514nm green laser, we only obtained the phonon modes of GaN. So applying 325nm Ar ion laser, we can observed the phonon modes spectra of both AlGaN and GaN layers. According to resonance conditions, the phonon modes of 789.74 cm-1 was origin from AlGaN alloy layer. The phonon modes of 740.89 cm-1 and 575.06 cm-1 were origin from GaN layer. Compared to other results, GaN layer was compress strain. We determined that AlGaN/GaN MQW interlayer relaxed strain stress from lattice mismatch, and phonon modes were clearly observed.