Carbon fiber composite (CFC) is widely used in structure design of space systems. Its stiffness design with little distortion is still a vital problem in the structure design of aerospace cameras. The design requirement of 2μm maximum distortion for CFC was achieved by the tolerance analysis of mechanical parts in a coaxial 3R optical system of space telescope. The physical model was established according to the force distribution of the whole structure. The CFC layer sequence was reasonably simplified based on the paprag theory for composite materials. MSC.Nastran was used to improve and verify the design. The result of the Finite Element Analysis (FEA) shows that the design of the CFC lens barrel meets the requirement of structure stiffness with maximum distortion of less than 2μm.