Abstract: The refractive index and absorption features of a novel polymer-cyclic olefin copolymers(trade names Topas COC) were studied in 0.1-3 THz band. With SolidWorks software, a common double-convex spherical lens of 100 mm focal length with effective aperture of 1.75 inches was designed, and then a set of mold for manufacturing the lens was designed. By hot compression molding, the Topas COC terahertz lens was fabricated, and the effects of heating temperature and time on the lens surface morphology was analyzed. The effects of the wavelength, thickness, radius of curvature and refractive index on focal length of the lens in the terahertz wavelength of 150 m, 300 m and 600 m was simulated and analyzed by using Zemax software. Studies have shown that the lens made by this method has surface smooth, high accuracy and defect-free structure, so the performance is very superior and meets linear and compact requirements of the terahertz system, and plays the role of collimating and focusing in the visible region and terahertz band.