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The species delimitation within Abies delavayi complex, consisting of A. delavayi Franch., A. fabri (Mast.) Craib, A. nukiangensis W. C. Cheng & L. K. Fu, and A. delavayi subsp. fansipanensis (Q. P. Xiang, L. K. Fu & Nan Li) Rushforth, has been a subject of long-term dispute. We combined different lines of evidence, including morphological characters, population-based mitochondrial DNA and chloroplast DNA sequences, and plastome data to assess its species delimitation. These four independent datasets revealed a consistent result that the four taxa of A. delavayi complex were hardly separated and could be regarded as one species. Our results further suggested that these four taxa might have experienced rapid morphological diversification, following a common expansion triggered by climate oscillations during the Pleistocene. In addition, we surveyed the phylogeographical history of A. delavayi complex as a whole based on ecological niche models and molecular data. These results consistently revealed that this high-mountain fir complex had experienced glacial expansion and interglacial contraction. Therefore, we propose that A. delavayi complex probably has undergone the phalanx expansion model in response to climate change during the Quaternary. Such expansion patterns demand consideration when establishing conservation strategies for threatened fir species.