The interactions between the harmonic source and a new energy power grid are harmful to the reliable operation of a power system and new energy consumption. It is critical to establish the harmonic source models and analyze the harmonic interactions to improve grid stability and power quality. In this paper, the harmonic problems in a new energy power grid are reviewed based on the principle of the modeling method and the mechanism of the harmonic interaction. First, according to different principles of modeling methods, the harmonic source modeling methods are divided into two categories, i.e., the mechanism and the data-driven modeling methods. The rationales, relative merits, and applications of different modeling methods are elaborated. Further, the harmonic interaction analysis and suppression methods are discussed. Finally, the current problems and future research orientations are introduced. This work is supported by the National Natural Science Foundation of China (No. 51777035).