四字格成語形式固定，意義深遠又饒富文化內涵，但先行研究卻鮮少突顯其習語性和規律性。本研究採構式語法 (construction grammar)，分析四字格成語於語法、語義及語用層面的習語性和規律性，以「一X#Y」（「#」表數字）的四字格構式為主要關注焦點，聚焦分析三個類型頻率 (type frequency) 最高的具體形式「一X 一Y」、「一X 二Y」和「一X 千Y」，並探討構式成語的語法功能。此外，本文除了從隱喻延伸 (metaphorical extension) 的角度來梳理嵌入成語構式的雙字詞和構式之間的互動關係外，也將探討不同構式之間互動的可能性。而「一例一休」和「一帶一路」等新創四字格，也顯示一個構式的類型頻率愈高，能產性愈強。換而言之，成語雖屬「固定詞組」，但在現代漢語，也同時具有某種程度的開放性與能產性。

Chinese four-character idioms possess structural uniformity, profound meaning and cultural connotation; however, the research in the field has failed to give sufficient prominence to their idiomaticity and regularity. Adopting the framework of “Construction Grammar,” in this article we discuss their interrelated syntactic, semantic, and pragmatic features by examining fourcharacter forms with the patterning [yi-X-#-Y] ‘one-X-number-Y’. In particular, we examine instances that fall under three specific prefabs with high type frequency: [yi- X-yi-Y] ‘one-X-one-Y’, [yi-X-er-Y] ‘one-X-two-Y’, and [yi-X-qian-Y] ‘one-Xthousand- Y.’ We also investigate their syntactic functions. In addition, we explore the relationships between X, Y, and the construction from the perspective of metaphorical extension, and investigate the interaction between different constructions. Newly created idioms such as [yi-li-yi-xiu] ‘One mandatory day off and one flexible rest day’ and [yi-dai-yi-lu] ‘The Belt and Road’ imply that the higher the type frequency of a construction, the higher its productivity. In other words, being classified as fixed phrases, idiomatic expressions have a certain degree of openness and productivity in Modern Chinese.