Liquid chromatography-mass spectrometry (LC-MS) has become one of the most important analytical techniques in modern times. It combines the high-efficiency separation capabilities of chromatography with the powerful structural identification capabilities of mass spectrometry, offering high sensitivity and excellent specificity. It has been widely applied in qualitative and quantitative analysis of complex systems. This review introduces the fundamental principles, instrument structure, and analytical methods of LC-MS, and discusses the applications of LC coupled with low-resolution mass spectrometry (LRMS) and high-resolution mass spectrometry (HRMS) in areas such as food safety, nutritional component analysis, omics analysis (e.g., proteomics, metabolomics), and environmental pollutant analysis. The latest advancements in LC-MS, including two-dimensional chromatography (2D-LC) and ion mobility separation (IMS) technologies, are also discussed.