As a representative work of the mid-western Shandong dialect in the early Qing Dynasty, Liaozhai Folk Song Collectionpreserves a substantial number of dialectal words and syntactic structures from the Ming and Qing periods. It comprehensively reflects the linguistic characteristic of the this area in Shandong over three centuries ago, serving as a crucial research material of early modern Chinese, particularly the grammar of the mid-western Shandong dialect during the Ming and Qing eras. This paper provides a detailed and meticulous analysis of the comparative “比” constructions and the superlative “比” constructions in the 15 folk songs from Pu Songling’s Liaozhai Folk Song Collection. It also reveals the structural characteristics, semantic relationships, and pragmatic features of the “比” constructions, supplementing and revising the incomplete and inaccurate descriptions in the diachronic research of the mid-western Shandong dialect, while also presenting the author's own perspectives. Furthermore, from both synchronic and diachronic perspectives, this study examines the increase and decline of this construction in the mid-western Shandong region, thereby clarifying the evolutionary trajectory and developmental patterns of the “比” constructions in the process of grammaticalization.