AlGaN based multiple-quantum-wells (MQWs) incorporating opposite polarity domains was grown by MOCVD. A direct demonstration of carrier localization effect was provided by a combination analysis of space-resolved luminescence peak position and Ga/Al composition distribution. Furthermore, through Raman spectroscopy, it is found that compressive strain plays a key role in improving the optical properties of UV-MQWs despite of the inferior crystalline quality in the N-polar domains. This suggests that incorporating sub-micrometer scale polarity domains in the MQWs is a promising perspective for the development of efficient UV emitters.