Cylindrical lenses have been widely used for collimating laser diode beam, but the collimating performance is usually not high. A new collimating element-double half-cylindrical lens (DHCL) was proposed. The theoretical expressions of the collimated beam of a DHCL are derived by transmission theory, and the numerical results are also given. Both theoretical and numerical results indicate that a DHCL can be made from the high refractive index material but a normal cylindrical lens cannot, and the collimating performance of a DHCL is much better than that of a normal cylindrical lens. The divergence angle of the collimated beam could be as small as 0.1 mrad.