A document surface micro-adjust mechanism for an optical scanner. The optical scanner has an outer casing with a transparent document platform in the upper section. An optical lens is enclosed inside the outer casing. The document surface micro-adjust mechanism uses a carrier chassis to embed the transparent document platform. One end of the carrier chassis is hinged upon the upper wall of the outer casing while the other end of the carrier chassis has a through hole to be engaged to a locking hole on a latching structure attached to the upper section of the outer casing. A locking element passes through the through-hole to engage with the locking hole. An elastic element is positioned between the carrier chassis and the latching structure. Depth of the locking element inside the locking hole may be adjusted to vary optical distance from the document surface of the transparent document platform to the optical lens inside the scanner.