Abstract: In recent years, a significant number of new energy units connected to the power grid adopt grid-following (GFL) control mode, which weakens the system's synchronization mechanism and has caused multiple stability problems due to insufficient frequency and voltage support capabilities. Comparatively, grid-forming (GFM) technology controls the converter as an equivalent voltage source, which can effectively provide voltage and frequency support, as well as improve the inertia and damping characteristics of the power grid. This paper summarizes the development history of common grid-forming technologies, analyzes and compares the principles of control modules of GFM converters with droop control, VSG control and matching control, and points out their essential differences from the grid-following control mode. Furthermore, by applying electromagnetic transient simulation tools, this paper compares transient response characteristics of the above several kinds of GFM/GFL control modes and demonstrates the advantage of GFM converters in realizing active support function. Finally, the difficulties and future research prospects of GFM technology are summarized.