Abstract: A method of measuring the thickness of plastic film based on capacitive sensor was introduced. By the no-contact means, an on-line continuous measurement system was designed. The block diagram of the system was shown to explain the principle the system works on. The principle of measuring the thickness of film using capacitive sensor was described. A vibration compensation solution by double eddy current sensors was proposed, aimed at the reduction of the error caused by the change of polar distance. The precision of system was increased. The scanning device was controled and the information of thickness was obtained by computer. Practice had proved the effectiveness of vibration compensation and the reliability of the system.