To study the influence of the placement process of the flexible FSS panels on the passband insertion loss of transmission window， several panels with different defects were designed and fabricated. The free-space transmission/reflection method was used to study the passband insertion loss of the panels at different incident angles. The results show the aperture makes the passband insertion loss increase by 0.3 dB， when incident angel is between 0° and 60°.The drape makes the passband insertion loss increase by 0.77 dB when incident angel is 0° and by 1.55 dB when incident angel is 60°； the dissymmetry make the passband insertion loss increase by 0.3 dB when incident angel is 0° and by 1.05 dB when incident angel is 60°. The drape has the greatest damage to the periodic structure， so it increases the passband insertion loss more significantly， and the passband insertion loss increases more obviously at large incident angle. The integrity of the flexible FSS panels should be avoided damage as far as possible in the placement process.