Abstract: To improve the accuracy of non-destructive thickness measurement,this paper presented a thickness-measurement method based on a capacitance sensor structure.Different from the traditional capacitance thickness-measurement system,it is a three-electrode capacitor system,containing three probes,which are in the same size and in millimeter size,besides,each is movable.Use conformal mapping theory and capacitance principle to establish mathematical model,programe algorithm in Fortran language.Compared with traditional methods,this method not only inherits the advantanges of traditional measurement system,simple structure,low power consumption,easy operation and control,low cost etc,but also has higher sensitivity,which is very important in thickness measurement.