Along with the exaltation of people to the electric energy quality requirements, the importance of compensating the reactive power is valued by people. The offset device of various kinds emerges with the tide of time. SVG plays an important part in the reactive compensating by the advantage of its quality. This text described the development, radical principle and control method of SVG and still introduced the limits, advantages and some improvement measures at the same time. Finally carry on analysis to the development tendency and lay foundation for the search of SVG technique.