The Changning- Menglian belt in western Yunnan is widely considered to be the remnants of Paleo- Tethys in this region and is of great significance in deciphering its evolution. However, understanding the relationship between lithostratigraphic units of different origins in this belt is a complex task. There are instances where strata of the same age exhibit drastically different lithology, while others show similar lithology despite having different ages. This complexity has posed a challenge to gaining a comprehensive understanding of the Paleo- Tethys evolution. The contents of some early- established formations were loosely defined due to the limitations of poor outcrops, complex structures, and a scarcity of large fossils. Consequently, these formations incorporated slices that were formed at different ages and environments. This is particularly true for the clastic formations previously assigned to the Permian. In this paper, we aim to analyze the contents of the Permian clastic formations established during the 1200,000 geological mapping conducted in the 1980s. Specifically, we focus on the Nanpihe Formation in the Gengma- Cangyuan area, located in the central- northern part of the belt, and the Laba Formation in the Lancang- Menglian area, situated in the southern part of the belt. We employ recent data on fossils, petrography, detrital zircon chronology, and extensive field observations to examine these formations. Our objective is to identify and organize the slices of different ages and lithology contained within the two formations. Additionally, we aim to redefine the content of the Nanpihe Formation, discuss the reasons for discontinuing the use of the Laba Formation as a distinct formation, and propose the naming of regionally identifiable succession slices within the Laba Formation after further in- depth study.