Abstract: A method for auto focus searching of optical microscopes is revealed. At first, sample a plurality of image signals according to a plurality of sampling positions. Then process the plurality of image signals to get a plurality of energy values. Next calculate a plurality of sharpness values of adjacent energy values and also calculate an absolute value corresponding to the sharpness value. Later check and find out a maximum value of the absolute values to get a sampling position corresponding to the image with the maximum value and use that position as the optimal focus position of the optical microscopes. By the sampling way, the energy values of the image signals are captured so as to save calculation time. Moreover, a sharpness value of adjacent energy value is also calculated so as to check the image captured at the best focus position quickly and reduce focus searching time of the optical microscope. Therefore, the focusing efficiency of the optical microscope is improved.