This paper analyzes the construction and control principle of Thyristor Switched Capacitor(TSC) and Active Power Filter(APF) integrated device. An harmonics detection method based on the instantaneous reactive power theory is also discussed. This method is effective to apply to TSC&APF integrated device and can get better result to eliminate the harmonics and compensate reactive power. A new integrated device which consists of TSC and APF is developed with this method. The application in the automobile industry shows that this device is correct and effective. It is a favorable model of improving the power quality and save the energy.