Lignin degradation is an important way to the utilization of biomass resources. Lignin is a three-dimensional networked macromolecular structure with many functional groups. When different methods are used to degrade lignin, detecting the content of phenolic hydroxyl groups in degraded lignin can more intuitively show the degradation efficiency of this method and can reflect the specific structure of lignin and the activities of hydrolysis, oxidation and reduction. Designing or comparing a measurement method that can efficiently and quickly determine the concentration of phenolic hydroxyl groups in degraded lignin is critical for analyzing the structure and function of small lignin molecules after depolymerization. According to the classification of instruments, the recent detection methods of phenolic hydroxyl groups after the degradation of lignin, such as titration methods, ultraviolet spectroscopy (ultraviolet spectrophotometry and Folin-Ciocalteu reagent, etc.), high-performance liquid chromatography, nuclear magnetic resonance (phosphorus spectrum, carbon spectrum, hydrogen spectrum, fluorine spectrum, etc.), gas chromatography-mass spectrometry, and gas chromatography (measurement of 1-acetylpyrrolidine by ammonolysis and methanol by periodate oxidation) were reviewed. Moreover, the application conditions, sample requirements and key factors of each quantitative analysis method were analyzed. Based on the efficient, convenient and economical detection method of phenolic hydroxyl, the future development direction prospected.