f-θ lens is the most important parts of laser marking system, its performance will affect the marking precision of laser marking machine directly. The design of f-θ lens is monochromatic light with 0.65 μm wavelength, negative barrel distortion is introduced in the design, field curvature is corrected and the Zifaer field curvature is equal to zero, image quality off axis and on axis is uniform, image plane is plane and the wave front aberrations is less than λ/4. The entrance pupil is placed at the object focus, so the image telecentric beam path is formatted, main light exited through the lens is parallel to the optical axis, the height of intersection points on image plane of main light are invariant, a linear scanning process is achieved in order to ensure scanning precision. The initial structure parameters of the lens are determined through the analysis of the primary aberration and the existing optical lens library, and then optimizes the design through ZEMAX software, the system with four pieces of ordinary spherical lens is obtained. This system is compact, short focal length and its performance is within diffraction limit, and has uniform illumination distribution, concentrated energy and small relative distortion, which meets marking requirements.