The service performance of internally coated epoxy resin composite steel pipes critically depends on the material and quality of their plastic coating layer. In response to the challenges posed by infrared spectroscopy identification difficulties arising from filler interference, poor surface conditions, or component migration in practical testing, this paper systematically compares the applicability of Attenuated Total Reflection (ATR) and potassium bromide (KBr) pellet-pressing methods in the analysis of plastic coating layers. The results indicate that the ATR method is simple to operate and suitable for rapid initial screening of samples with clean surfaces and minimal filler interference. Conversely, the KBr pellet pressing method effectively eliminates surface selectivity effect, clearly presenting the characteristic absorption peaks of the bulk resin and additives (such as phthalate plasticizers, calcium carbonate, barium sulfate, etc.), making it particularly suitable for arbitration analysis of complex formulations or poor-quality ATR spectra. Based on this, this paper establishes a standardized infrared identification process of "ATR initial screening - KBr verification", and verifies the reliability of this process in identifying bisphenol A epoxy resin, polyester-epoxy hybrid systems, and other aspects through typical samples. The research findings provide practical and efficient analytical technical support for quality control, failure analysis, and market supervision of internally coated composite steel pipes.