Terahertz imaging technology is a rising detection technology with great development prospects. In order to satisfy the requirement for terahertz detector array imaging,a compact refractive optical lens is designed. The lens material is HRFZ-Si with a parylene anti-reflection coating on the surface. The imaging on the focal plane of the point at infinity on the axis and off axis through the optical lens is simulated by using Tracepro software,and the structural parameters of the optical lens are optimized. The optimizing lens simulation results indicate that the focal length of the optical lens is 26.2mm,the filed angle is 16.3°,the relative aperture is 1.9∶1 and the resolution is 20 lp/mm.