A method for reactive compensation by using thyristor switching device to change the capacitor voltage directly and the wiring of the principle are proposed. The main calculations for a number of 10kV small capacity device’s parameters and the tap-changing control method are also analysised. Conducted a simulation by MATLAB/Simulink for the transient characteristics of corresponding voltage and current in the tap changing process, indicating that the device can adjust capacitive reactive power in multi-stages and large scale, transient performance in grade-changing process is good. The project costs lower than other fast reactive compensation devices,and this equipment can be widely used in high voltage power network..