Long-chain linear alkylbenzenes (LABs) are essential precursors to produce alkylbenzene sulfonates, which have high surfactant properties and are readily biodegradable, widely used in various detergents. However, an effective and rapid method for the direct analysis and quality control of LAB chemical composition still needs to be improved. This study uses high-performance liquid chromatography coupled with microwave plasma torch mass spectrometry (HPLC-MPT-MS) to analyze the composition of long-chain LABs and quantify nine of these components. The results show that the main components in long-chain LAB samples are eicosylbenzene, docosylbenzene, and tetracosylbenzene, primarily including four structures, three of which have been structurally identified. This study successfully separates and analyzes LAB directly via HPLC-MPT-MS, providing a valuable and reliable method for the quality evaluation of LAB.