A light spot converter from a circular face to a circle——a transparent glass cone is presented.The light propagation characteristics and light spot converter principles inside a cone are studied based on the principle of total reflection of light.The light propagation characteristics and the effect of converting light spot from a circular face to a circle through a cone are simulated by using the ray tracing method.The results show that when the cone angles are equal to a series of special values incident beams normal to the bottom surface of a cone passing through this cone will exit along its generatrices,and form a circle-type spot on the plane perpendicular to the axis of cone,all its energies is concentrated in the circle.A light spot converter from circular face to circle can be used in conjunction with the lens so as to only convert light spot mode and not change the beam propagation direction.The light spot converter has the advantages of simple structure and low energy-loss,and easy fabrication.