Abstract: The heat shrinkable sleeves composed of radiation cross-linked polyethylene layer, hot-melt adhesives and matching liquid epoxy primer is most widely used in the joint coating material in 3PE pipeline. During the joint coating process of heat shrinkable sleeves, PE layer of the main pipe and the epoxy primer on both sides of the weld seam form effective bonding with heat shrink sleeves through the action of hot-melt adhesives, and the structural stability of hot-melt adhesives will have a major impact on the long-term effectiveness of heat shrinkable sleeves joint coating. For this purpose, the impact of hygrothermal ageing on chemical structure stability of hot-melt adhesive is studied for 5 typical joint coating heat shrinkable sleeves at home and abroad with infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC) method, etc. The results show that hygrothermal ageing cause significant structural changes in components of hot melt adhesive, that is, there exists partial hydrolysis of ester groups and small molecules removal and there exists degradation/ cross-linking reaction in some components.