In order to solve the problem that there exists astigmatism during the fabrication of carbon fiber reinforced polymer(CFRP) reflective mirror, a theoretical model was established to explain the relations, and relative experiments were made to verify the model. First, from classical laminate thermal effect theory, ply angle misalignment and temperature variation during manufacturing process were considered. The corresponding formulas were deduced to demonstrate that the surface of CFRP reflective mirror existed astigmatism under thermal effect because of ply angle misalignment. Two groups of samples with respective ply sequence [0° 90° 45° -45°]2s and [(0° 90° 45° -45°)s]2 were manufactured and their astigmatism were measured with a Zygo long-wave infrared interferometer(λ=10.6 μm). Experimental results indicate that average astigmatism RMS of the front group is 0.034λ, and average astigmatism RMS of the latter group is 0.510λ. It verifies that one of the main reasons causing astigmatism of CFRP reflective mirror is ply angle misalignment, and the degree of astigmatism will decrease by increasing quasi-isotropy of bending stiffness.