Abstract: An infrared inverted telephoto objective is designed. Based on the characteristics of infrared objective, a miniaturization design is analyzed based on Gauss optics. The parameters of the optical system are given. Its focal length is 10mm, F/# is 1.2 and field of view is 60. The system consists of 4 pieces of silicon lens and 2 second order aspheric surface, and its MTF is more than 45% at the cutoff frequency. The length of the optical system is shorter than 57 mm, and its diameter is less than 24 mm. The system is compact in size, cost effective and easy to be assembled，and it provides good performance from -40℃ to 60℃.