The invention provides an offline processing method for metal film thickness data in a whole CMP (Chemical Mechanical Planarization) process. The offline processing method comprises the following steps: reading an output signal of an electric eddy sensor, and calculating a sampling signal according to the output signal; setting an amplitude threshold value of the sampling signal; traversing all sampling signals to obtain all non-zero point signal sections according to the amplitude threshold value; calculating the signal width of each non-zero point signal section, and determining a width threshold value of the sampling signals according to the signal width; traversing all non-zero signal sections in a measurement process again according to the amplitude threshold value and the width threshold value, extracting an effective measurement signal section, and calculating an average value of all data points in a central interval of each effective measurement signal section; acquiring the change information of metal film thickness in the whole CMP process according to the average value. According to the offline processing method, the influence of an interference signal and part abnormal signals in the measurement process can be effectively eliminated; a real copper layer thickness change can be calculated concisely and effectively; moreover, the calculation result accuracy is high.