Magnetic field modulated permanent magnet vernier generators (PMVGs) show great potential in the field of new energy generation (e.g., wind power, wave energy conversion, etc.) due to their advantages of low-speed direct drive and high torque density. In this paper, the development history, typical topologies and key technologies of magnetic field modulated PMVGs are systematically reviewed. From traditional permanent magnet vernier motors, linear vernier motors, superconducting vernier motors to hybrid excitation and fault-tolerant designs, various types of structures have improved the power density and operating efficiency through air-gap magnetic field modulation, pole-slot fit optimization, etc., but they also face the challenges of low power factor, iron core saturation, and high AC losses. Research shows that intelligent algorithm optimization, modular design and the introduction of superconducting materials can significantly improve the performance of motors. In the future, it is necessary to further explore the synergistic optimization of multi-objectives, the application of new materials and the reliability enhancement under complex working conditions, in order to promote its large-scale application in more industrial scenarios.