In a focus identification method for identifying different focuses of an object, discrete image data is acquired from captured images of an object. The images are captured by a charge coupled device (CCD) in motion of a measurement machine at a predetermined time period. The discrete image data includes definitions of the images and Z-coordinates of the CCD when capturing the images. Maxima and minima of the discrete image data are computed to establish intervals within the discrete image data. The intervals are selected one by one, and a curve is fitted according to the discrete image data at the selected interval. A peak value of the fitted curve is computed as one of focuses of the object when a goodness of fit of the fitted curve meets a predetermined criterion.