With the development of society, power electronic devices have been widely used in daily life, resulting in an increasing content of harmonics in the power grid, polluting the operation quality of the power grid, threatening the safe and stable operation of the power grid, greatly affecting the surrounding electrical environment, and becoming one of the main public safety hazards of the power grid at present. Therefore, quickly and accurately detecting harmonics in the power grid has become the key to solving the problem of harmonic pollution. The primary task in solving harmonic problems is to accurately detect the components, amplitude, phase, and other information of harmonics. This article comprehensively elaborates on the main causes of harmonic generation and the current main methods of harmonic detection. The method of harmonic detection determines the accuracy and speed of harmonic detection. This article focuses on analyzing harmonic detection methods based on instantaneous reactive power theory, neural network-based harmonic detection methods, and wavelet transform based harmonic detection methods, and analyzes the current problems and future development trends of harmonic detection.