This research project proposes a phonetic-phonological study of the realization of diphthongs in Mandarin spoken in three regions: Beijing, Tianjin and Xi’an. I will first look at the phonetic representations of the diphthongs in these regional varieties and statistically analyze the factors influencing the monophthongization of diphthongs with modeling approaches, such as GAMMs and Random Forests. In so doing, I will take into account of sociophonetic factors such as regional variety accounts. I will then make an evaluation of the mechanism of the interaction between the F0 and the realization of diphthongs in all three varieties, in both the monosyllabic case and the continuous speech case, and discuss the difference between the two types of diphthongs – the rising ones and the falling ones – within the framework of Articulatory Phonology (following Browman & Goldstein, 1992, 2000).