The invention relates to a digital microscope and a focusing method thereof. According to the digital microscope and the focusing method thereof of the invention, a focusing lens group, a zoom lens group and corresponding control circuits are integrated in a microscope; a main control unit in the microscope executes a focusing search algorithm and a focusing tracking algorithm so as to control the focusing lens group and the zoom lens group to move; and the microscope is made to realize automatic focusing through adjusting an image distance; and the microscope is made to realize zoom through changing a focal length. With the digital microscope and the focusing method thereof of the invention adopted, automatic focusing can be realized without moving an object stage and the microscope, and focusing efficiency is improved, and focusing time is shortened; and a zoom tracking algorithm is adopted, so that continuous zoom and tracking can be realized, and images are clear in a whole zoom process. According to the digital microscope and the focusing method thereof of the invention, an exposure algorithm is executed through the main control unit, and the brightness of an auxiliary light source at the front end of the microscope can be automatically adjusted through the change of luminous flux, and therefore, uniform exposure can be realized.