Post Focus Compression (PFC) has been recognized as a potential typological tool for classifying languages into different language families. While its function has been well-documented in monolingual speakers, the dynamics of PFC in bilingual speakers remain less explored particularly when two languages with PFC (+PFC) are in contact. This study aims to fill this gap by investigating PFC in bilingual speakers of Standard Mandarin (MA) and Yangzhou Mandarin (YZ), two +PFC languages. Twelve bilingual Mandarin-Yangzhou speakers were recruited for a language background questionnaire and an experiment of producing both MA and YZ using a question-answer paradigm. Their F0, duration, and intensity were recorded for analysis. We found that proficiency in YZ was positively correlated with the presence of PFC in YZ and the loss of PFC in MA, while proficiency in MA showed the opposite trend. These findings indicate that when two +PFC languages interact in the same context, PFC is highly sensitive to the speakers' proficiency in each language, even for bilinguals. This study thus contributes to our understanding of the dynamics of PFC in bilingual speakers and its future applications in linguistic typology.