Freeform surfaces provide more design freedoms to imaging system without introducing new types of aberrations,
therefore better performance can be expected. In this paper, the design of a four-mirror telescope with freeform surfaces
was introduced and issues such as tolerancing , manufacturability were discussed; Based on that, fabrication and testing
of freeform surfaces were discussed; Particularly direct CNC generation, deterministic polishing techniques including
CCOS, MRF and IBF Polishing were presented in detail. Since testing is critical to make high accurate freeform surfaces,
the paper focused on Computer Generated Hologram (CGH) design and implement to measure large freeform mirrors. In
particular, correction of detector to mirror mapping distortion was discussed in detail. Finally, the full field alignment
results were given to show the feasibility of using large freeform surfaces in space optics.