Flax, a crucial fiber crop, exhibits excellent textile properties and serves as a model plant for investigating phloem fiber development. The regulation of multiple genes significantly influences fiber development, notably involving NAC (NAM, ATAF1/2, CUC2) transcription factors in forming the fiber secondary cell wall (SCW). Overexpressing LuNAC61in flax resulted in sparse top meristematic zone leaves and significantly decreased stem cellulose content. Scanning electron microscopy and staining observations revealed a significant reduction in fiber bundles. GUS staining analysis demonstrated high activity of the LuNAC61promoter in the flax stem’s bast fibers. Additionally, several members of the LuPLATZand LuCesAfamilies exhibited significant coexpression with LuNAC61. Subcellular localization indicated LuPLATZ24 protein presence in the nucleus and cytoplasm, LuNAC61 protein exclusively in the nucleus, and LuCesA10 in the nucleus and endoplasmic reticulum. LuPLATZ24positively regulates LuNAC61, whereas LuNAC61negatively affects LuCesA10, suggesting the involvement of a metabolic network in regulating flax fiber development. In conclusion, our study provides a critical opportunity for a comprehensive and in-depth analysis of the mechanisms governing flax fiber development and the potential use of biotechnology to enhance flax fiber yield.