In order to deal with the threat of space debris to space experiment platforms and equipment, three-mirror anastigmatic system, which has the characteristics of light weight, small size and good optical performance, are used for space debris detection and detailed imaging. With the development of freeform surfaces, this article shows a new type of structure which has good optical performance and simple complexity of assembly and adjustment. The first step is to analyze the calculation method of the initial structure parameters of TMA system, and then the secondary mirror adopts the XY polynomial freeform surface. The primary mirror is reused as tertiary mirror, and the design of a new type TMA system is finally completed. Its effective focal length is 400 mm, the field of view (FOV) is 2°×4°, F/# is 5. At the Nyquist frequency 108lp/mm, the MTF value of this system is greater than 0.588. The maximum distortion is less than 0.80%. The results show that the imaging quality of the system meets the design requirements in the effective field of view. © 2021 SPIE