Based on the optical readout method with knife edge filter, the relationship between the optical detection sensitivity and reflector length was discussed under the circumstance that the reflector was bent. Analysis indicates that the optical sensitivity increases with the reflector's lengthening at first, then it reaches a maximum value, and then it decreases as the reflector continues to lengthen. For the reflectors with different curvature radii and lengths, analysis shows that the sensitivity will reach a maximum value when the expression L 2 /R=λ ( L is length of reflector, R is curvature of the reflector, λ is wavelength of illumination light) is satisfied. The optical detection sensitivities of the fabricated FPAs with different pixel sizes as 200μm, 120μm and 60μm were obtained experimentally. The result coincides with the theoretical analysis.