The grid-connected inverter is the key core component of new energy power generation systems. Acting as the bridge connecting new energy sources to the grid, it converts the direct current (DC) generated by wind and solar power into power-frequency AC electricity acceptable to the grid. Grid-connected inverters have become a critically important interface device between new energy sources and the power system, and their grid-connection performance directly determines the utilization efficiency of new energy and the stability of the grid. Since the interaction between inverters and grid impedance can cause harmonic pollution, and excessive grid impedance can also destabilize the inverter system, the power quality and stability issues caused by inverters are becoming increasingly important. This paper systematically elaborates on the main mechanisms and analysis methods for harmonic generation in inverters. Based on the harmonic frequencies produced, they are categorized into two types: low-frequency harmonics and switching harmonics. The former are mainly caused by the dead-time effect, while the latter result from inherent defects in the modulation strategy itself. Through a systematic review of existing research on improvements in harmonic mechanism analysis and suppression techniques, this paper delves deeply into the key technical bottlenecks in the field of harmonic mechanism analysis and suppression, providing theoretical references and technical guidance for research in related fields.