This study aims to document the pronunciation status and methods of Mandarin by intermediate-level learners in order to meet the practical requirements of high-precision phonetic recognition for these learners. The research investigates the formant resonance patterns and acoustic vowel charts of Mandarin pronunciation by intermediate-level learners, calculating the Euclidean distance and vowel duration parameters in both standard and non-standard Mandarin for each vowel. The trajectory and pronunciation morphology of the learners acquiring Mandarin monophthongs were thus derived. Notably, it was discovered that the Euclidean distance between the basic vowels of intermediate-level learners and native Mandarin speakers generally decreases as proficiency in Mandarin increases. Additionally, it was observed that, during the process of Mandarin acquisition by learners, there were both "similar vowels" and "unfamiliar vowels" which presented varying degrees of acquisition ease, and certain phenomena that neither the Contrastive Analysis Hypothesis (CAH) nor the Speech Learning Model (SLM) could predict.