The torque on a specially shaped micro object produced by a vortex beam is studied based on a ray-optic (RO) model. Based on conservation of momentum and orbital angular momentum, the formulas for the torque along x, y and z directions are derived. The numerical calculation is given to show the dependence of the optical torques on the inclination angle of the micro object. It is shown that the torque is dependent upon both the light momentum and orbital angular momentum (OAM) of the incident vortex beam. We can control the rotation of the micro object by modulating the topological charge of the incident light beam. Moreover we can make the micro object stop.