1. A focus identification method, the method being executed by at least one processor of a computing device, the method comprising: acquiring discrete image data from a plurality of images of an object, wherein the plurality of images are captured by a charge coupled device (CCD) of a measurement machine every a predetermined time period when the CCD moves along a Z-axis of the measurement machine at a fixed speed, and the discrete image data comprises definitions of the plurality of images and Z-coordinates of the CCD when capturing the plurality of images; computing maxima and minima of the discrete image data; establishing intervals of the discrete image data according to the maxima and minima; selecting an interval from the established intervals one by one; fitting a curve according to the discrete image data in the selected interval, and computing a mathematical expression of the fitted curve; and computing a peak value of the fitted curve as one of focuses of the object according to the mathematical expressions, and storing the mathematical expressions and the peak value into a storage device of the computing device upon condition that a goodness of fit of the fitted curve meets a predetermined criterion.