Abstract: An embodiment disclosed bevel-axial auto-focusing method for a microscopic system, including: capturing full-frame bevel-axial input image; using image analysis to read image information and transmitting grayscale information to a statistic analysis module; the statistic module extracting image statistic characteristics and performing curve fitting with probability function; and estimating the optimal focus point based on the post-fitting characteristic parameters. A preferred embodiment combines image with Gaussian curve fitting and Kalman filter, and analyzes the in-focus position based on image quality so as to directly determine the optimal rectification value of the in-focus position on the object surface. The method can improve the accuracy and speed of auto-focusing.