The invention relates to a laser direct-writing system and a photolithography method. The laser direct-writing system comprises a focal length measurement system and an exposure system, wherein the focal length measurement system adopts an offline way to measure the three-dimensional shape information of the surface of a whole object to be etched, then converts the three-dimensional shape information into focusing information and sends the focusing information to the exposure system; according to the focusing information, in the process that the surface of the object to be etched is photoetched, the exposure system regulates the focal length so as to suit the concave and convex degree of the surface of the object to be etched, and an exposure point always focuses on the surface of the photoetched object.