This paper reports the use of theory of geometrical optics to analyze how an optical field interacts with a cylindrical object. Of great interest is the mechanism with which a laser beam with a special profile manipulates a particle which has a similar shape as the beam profile. The present paper investigates the interaction between a cylinder-shape fiber and a laser beam with a line-shape profile. Based on the Fresnel equation, a numerical model was formulated to describe the optical torque generated by a projected line-shape optical image. The drag force was also considered in the model to accurately describe the fiber's movement in a liquid. A differential equation is established to describe this damped movement of the cylinder. Parametric analysis was carried out to investigate the influence of the beam power and the liquid viscosity as well as the density, the length, and the diameter of the cylindrical object. The movement of a carbon fiber was measured with a CCD camera. The observed experimental results agree well with the theoretical results.