This study investigates the transfer effect of dialect and Mandarin on English monophthongs acquisition and compares acoustic features of English monophthongs by English as a Foreign Language (EFL) learners from Harbin (HEB), Changchun (CC), Shenyang (SY) and Dalian (DL), which belong to northeast region of China, in comparison with native English speakers, from the spectral perspective. Ten English monophthongs (/α, Λ, i, I, u, ℧, æ, Λ, Ɔ,3 /) and all monophthongs of dialect and Mandarin are investigated. An acoustic analysis results show that α produced by HEB and CC learners is more affected by dialect, /i/ produced by SY learners is affected by Mandarin, 3 / produced by HEB, CC and DL learners is affected by similarly pronounced monophthong $/\alpha/$ in dialect. These results can be explained by the Speech Learning Model (SLM). On the other hand, /u/ produced by learners from all four cities is similar to that of the native English speakers. In conclusion, both dialect and Mandarin exhibit a transfer effect on EFL Learners’English monophthongs acquisition.